Consolidated Statement of Shareholders' Equity Statement - USD ($) $ in Thousands	Total	Common Stock [Member]	Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income [Member]
Balances at Dec. 31, 2016					$ (24,400)
Net income	$ 34,970
Other comprehensive loss	7,660				7,660
Shares surrendered upon exercise and vesting of equity awards to cover taxes	(480)
Balances at Sep. 30, 2017					(16,740)
Balances at Dec. 31, 2017	544,020	$ 460	$ 823,850	$ (262,960)	(17,330)
Net income	66,590			66,590
Other comprehensive loss	(1,550)				(1,550)
Purchase of common stock	(3,590)		(3,590)
Shares surrendered upon exercise and vesting of equity awards to cover taxes	(2,380)		(2,380)
Non-cash compensation expense	4,400		4,400
Balances at Sep. 30, 2018	$ 607,490	$ 460	$ 822,280	$ (196,370)	$ (18,880)