Rhapsody Joint Venture (Additional Information) (Detail) - USD ($)	1 Months Ended		3 Months Ended			9 Months Ended		12 Months Ended
	Jan. 31, 2017	Dec. 31, 2016	Sep. 30, 2017	Sep. 30, 2016	Mar. 31, 2010	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Dec. 01, 2016
Schedule of Equity Method Investments [Line Items]
Losses recorded in the operations of Rhapsody			$ 0	$ 233,000		$ 1,097,000	$ 629,000
Advance to Rhapsody						$ 1,500,000	0
Rhapsody America LLC
Schedule of Equity Method Investments [Line Items]
Percentage of ownership interest in Rhapsody			42.00%			42.00%
Payments for restructuring					$ 18,000,000
Liquidation preference amount			$ 10,000,000.0			$ 10,000,000.0
Losses recorded in the operations of Rhapsody			0	$ (200,000)		1,100,000	$ 600,000
Carrying value			0			0
Loan principal to related party									$ 5,000,000
Advance to Rhapsody	$ 1,500,000							$ 3,500,000
Related party loan rate		10.00%
Maximum allowable cross default allowed before receivables become immediately due			$ 1,000,000			$ 1,000,000