Annual report pursuant to Section 13 and 15(d)

Acquisitions and Recent Transactions - Summary of Business Acquisitions and Asset Purchased (Detail)

v3.19.1
Acquisitions and Recent Transactions - Summary of Business Acquisitions and Asset Purchased (Detail) - USD ($)
 12 Months Ended
Apr. 19, 2018
Aug. 31, 2017
Jul. 06, 2017
Jun. 08, 2017
Mar. 15, 2017
Dec. 31, 2018
Dec. 31, 2017
Acquisition Date [Line Items]              
Business acquisition           $ 11,180,000 $ 4,043,000
KTRB-AM, San Francisco, California (Asset Purchase) [Member]              
Acquisition Date [Line Items]              
Asset purchase           $ 5,349,000  
Business acquisition, Effective Date of Acquisition           Sep. 11, 2018  
Hilary Kramer Financial Newsletter (Business Acquisition) [Member]              
Acquisition Date [Line Items]              
Business acquisition           $ 439,000  
Business acquisition, Effective Date of Acquisition           Aug. 09, 2018  
Just1Word (Business Acquisition) [Member]              
Acquisition Date [Line Items]              
Business acquisition           $ 312,000  
Business acquisition, Effective Date of Acquisition           Aug. 07, 2018  
KZTS-AM (formerly KDXE-AM), Little Rock, Arkansas (asset purchase) [Member]              
Acquisition Date [Line Items]              
Asset purchase           $ 210,000  
Business acquisition, Effective Date of Acquisition           Jul. 25, 2018  
Childrens-Ministry-Deals.com (Business Acquisition) [Member]              
Acquisition Date [Line Items]              
Business acquisition           $ 3,700,000  
Business acquisition, Effective Date of Acquisition           Jul. 24, 2018  
KDXE-FM (Formerly KZTS-FM), Little Rock, Arkansas (Business Acquisition) [Member]              
Acquisition Date [Line Items]              
Business acquisition           $ 1,100,000  
Business acquisition, Effective Date of Acquisition           Jun. 25, 2018  
HearItFirst.com (Asset Purchase) [Member]              
Acquisition Date [Line Items]              
Asset purchase $ 70,000         $ 70,000  
Business acquisition, Effective Date of Acquisition           Apr. 19, 2018  
WWRC-AM Formerly WSPZ-AM in Bethesda, Maryland Business Acquisition [Member]              
Acquisition Date [Line Items]              
Business acquisition             $ 620,000
Business acquisition, Effective Date of Acquisition             Nov. 22, 2017
Real Property of Radio Station WSPZ-AM in Bethesda, Maryland Business Acquisition [Member]              
Acquisition Date [Line Items]              
Business acquisition             $ 1,500,000
Business acquisition, Effective Date of Acquisition             Sep. 15, 2017
Teacher Tube.com Business Acquisition [Member]              
Acquisition Date [Line Items]              
Business acquisition   $ 1,100,000         $ 1,100,000
Business acquisition, Effective Date of Acquisition   Aug. 31, 2017         Aug. 31, 2017
Intelligence Reporter Newsletter Business Acquisition [Member]              
Acquisition Date [Line Items]              
Business acquisition   $ 2,500,000          
Business acquisition, Effective Date of Acquisition   Aug. 31, 2017         Aug. 31, 2017
FM Translator Construction Permit, Eaglemount, Washington Asset Acquisition [Member]              
Acquisition Date [Line Items]              
Business acquisition             $ 40,000
Business acquisition, Effective Date of Acquisition             Jul. 24, 2017
TradersCrux.com Business Acquisition [Member]              
Acquisition Date [Line Items]              
Business acquisition     $ 300,000       $ 298,000
Business acquisition, Effective Date of Acquisition     Jul. 06, 2017       Jul. 06, 2017
FM Translator Construction Permit, Festus, Missouri Asset Acquisition [Member]              
Acquisition Date [Line Items]              
Business acquisition             $ 40,000
Business acquisition, Effective Date of Acquisition             Jun. 28, 2017
Portuguese Bible Mobile Applications Business Acquisition [Member]              
Acquisition Date [Line Items]              
Business acquisition       $ 65,000     $ 82,000
Business acquisition, Effective Date of Acquisition       Jun. 08, 2017     Jun. 08, 2017
Prayers for Special Help Business Acquisition [Member]              
Acquisition Date [Line Items]              
Business acquisition         $ 200,000   $ 245,000
Business acquisition, Effective Date of Acquisition         Mar. 15, 2017   Mar. 15, 2017
FM Translator Construction Permit, Quartz Site, Arizona Asset Purchase [Member]              
Acquisition Date [Line Items]              
Business acquisition             $ 20,000
Business acquisition, Effective Date of Acquisition             Mar. 14, 2017
FM Translator Construction Permit, Roseburg, Oregon Asset Purchase [Member]              
Acquisition Date [Line Items]              
Business acquisition             $ 45,000
Business acquisition, Effective Date of Acquisition             Mar. 01, 2017
FM Translator, Astoria, Oregon Asset Purchase [Member]              
Acquisition Date [Line Items]              
Business acquisition             $ 33,000
Business acquisition, Effective Date of Acquisition             Jan. 16, 2017
FM Translator Construction Permit, Mohave Valley, Arizona Asset Purchase [Member]              
Acquisition Date [Line Items]              
Business acquisition             $ 20,000
Business acquisition, Effective Date of Acquisition             Jan. 01, 2017