Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Paid-In Capital	Accumulated Other Comprehensive Loss	Retained Earnings	Treasury Stock
Beginning balance at Dec. 31, 2014	$ 625,458	$ 992	$ 521,228	$ (31,992)	$ 262,616	$ (127,386)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(90,828)				(90,828)
Employee stock options, restricted stock and employee stock purchase plan	(1,007)	2	(402)			(607)
Stock-based compensation expense	14,202		14,202
Income tax effect, net, of employee stock related activity	(412)		(412)
Foreign currency translation adjustments	(26,284)			(26,284)
Other	(870)		(870)
Ending balance at Dec. 31, 2015	520,259	994	533,746	(58,276)	171,788	(127,993)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(40,712)				(40,712)
Employee stock options, restricted stock and employee stock purchase plan	230	4	(478)		(1,203)	1,907
Stock-based compensation expense	12,056		12,056
Income tax effect, net, of employee stock related activity	(1,558)		(1,558)
Foreign currency translation adjustments	(4,932)			(4,932)
Issuance of Convertible Notes due 2021	15,200		15,200
Ending balance at Dec. 31, 2016	500,543	998	558,966	(63,208)	129,873	(126,086)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(6,148)				(6,148)
Employee stock options, restricted stock and employee stock purchase plan	(185)	14	1,636		(350)	(1,485)
Stock-based compensation expense	10,843		10,843
Income tax effect, net, of employee stock related activity	(500)
Foreign currency translation adjustments	9,989			9,989
Issuance of shares for acquisition	32,438	34	32,404
Ending balance at Dec. 31, 2017	$ 547,480	$ 1,046	$ 603,849	$ (53,219)	$ 123,375	$ (127,571)