Revenue Recognition - Effect on Financial Statements (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Other current assets	$ 1,275		$ 1,275		$ 4,098	$ 4,335
Intangible, equity method investment and other assets, net	20,244		20,244		20,792	20,949
Accumulated deficit	(7,057)		(7,057)		$ (11,731)	(11,337)
Deferred income tax liability, net	12,271		12,271			12,886
Selling, general and administrative expenses	16,712	$ 16,328	47,317	$ 47,357
Income tax provision (benefit)	(194)	1,067	1,600	758
Net income (loss)	61	$ 1,751	4,674	$ 1,688
Calculated under Revenue Guidance in Effect before Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Other current assets	1,492		1,492			4,335
Intangible, equity method investment and other assets, net	20,244		20,244			20,949
Accumulated deficit	(7,319)		(7,319)			(11,337)
Deferred income tax liability, net	12,316		12,316
Selling, general and administrative expenses	16,771		47,495
Income tax provision (benefit)	(209)		1,555
Net income (loss)	19		4,546
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]
Other current assets	(217)		(217)			(237)
Intangible, equity method investment and other assets, net	0		0			(157)
Accumulated deficit	(262)		(262)			$ (394)
Deferred income tax liability, net	(45)		(45)
Selling, general and administrative expenses	(59)		(178)
Income tax provision (benefit)	15		45
Net income (loss)	$ 42		$ 128