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Revenue Recognition - Impact of ASC 606 Adoption (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Assets
Other non-current assets	$ 2,512		$ 2,512		$ 1,636
Liabilities
Deferred income taxes	12,143		12,143		12,043
Stockholder's equity
Retained earnings	78,156		78,156		124,442
Operating expenses
Selling, general and administrative expenses	56,142	$ 57,186	176,312	$ 165,855
Loss from operations	(43,212)	11,585	(39,617)	30,736
Income (loss) before taxes	(45,263)	10,844	(46,070)	26,612
Income tax benefit	(326)	3,728	851	9,444
Net (loss) income	$ (44,937)	$ 7,116	$ (46,921)	$ 17,168
Basic earnings (loss) per share (in dollars per share)	$ (0.87)	$ 0.13	$ (0.90)	$ 0.32
Diluted earnings (loss) per share (in dollars per share)	$ (0.87)	$ 0.13	$ (0.90)	$ 0.31
Capitalized contract costs amortization	$ 300		$ 100
Adjustments
Assets
Other non-current assets	(619)		(619)
Liabilities
Deferred income taxes	(167)		(167)
Stockholder's equity
Retained earnings	(452)		(452)
Operating expenses
Selling, general and administrative expenses	(9)		(30)
Loss from operations	9		30
Income (loss) before taxes	9		30
Income tax benefit	2		8
Net (loss) income	$ 7		$ 23
Basic earnings (loss) per share (in dollars per share)	$ 0		$ 0
Diluted earnings (loss) per share (in dollars per share)	$ 0		$ 0
As Adjusted Without Adoption of ASC 606
Assets
Other non-current assets	$ 1,893		$ 1,893
Liabilities
Deferred income taxes	11,976		11,976
Stockholder's equity
Retained earnings	77,704		77,704
Operating expenses
Selling, general and administrative expenses	56,133		176,282
Loss from operations	(43,203)		(39,587)
Income (loss) before taxes	(45,254)		(46,040)
Income tax benefit	(324)		859
Net (loss) income	$ (44,930)		$ (46,899)
Basic earnings (loss) per share (in dollars per share)	$ (0.87)		$ (0.90)
Diluted earnings (loss) per share (in dollars per share)	$ (0.87)		$ (0.90)
Accounting Standards Update 2014-09
Stockholder's equity
Retained earnings					$ 500