Revenue Recognition - Effect on Financial Statements (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Selling, general and administrative expenses	$ 15,857	$ 15,560	$ 30,605	$ 31,029
Other current assets	1,874		1,874		$ 4,098	$ 4,335
Intangible, equity method investment and other assets, net	20,469		20,469		20,792	20,949
Accumulated deficit	(7,118)		(7,118)		$ (11,731)	(11,337)
Deferred income tax liability, net	12,301		12,301			12,886
Income tax provision (benefit)	1,732	882	1,794	(309)
Net income (loss)	4,452	$ 1,724	4,613	$ (63)
Calculated under Revenue Guidance in Effect before Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Selling, general and administrative expenses	15,916		30,723
Other current assets	2,111		2,111			4,335
Intangible, equity method investment and other assets, net	20,508		20,508			20,949
Accumulated deficit	(7,427)		(7,427)			(11,337)
Deferred income tax liability, net	12,334		12,334
Income tax provision (benefit)	1,715		1,761
Net income (loss)	4,410		4,528
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Selling, general and administrative expenses	(59)		(118)
Other current assets	(237)		(237)			(237)
Intangible, equity method investment and other assets, net	(39)		(39)			(157)
Accumulated deficit	(309)		(309)			$ (394)
Deferred income tax liability, net	(33)		(33)
Income tax provision (benefit)	17		33
Net income (loss)	$ 42		$ 85