Unaudited Condensed Consolidated Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Shares	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning balance (in shares) at Dec. 31, 2016		29,785
Beginning balance at Dec. 31, 2016	$ 535,637	$ 8,934	$ 336,756	$ 218,947	$ (29,000)
Adoption of new accounting principle	995			995
Net loss	(104,122)			(104,122)
Foreign currency translation adjustment, net of tax	7,512				7,512
Foreign currency hedge, net of tax	(988)				(988)
Change in defined benefit pension plan net actuarial loss, net of tax	42				42
Issuance of convertible debt, net of tax	8,458		8,458
Non-cash compensation	5,846		5,846
Vesting of stock awards (in shares)		41
Vesting of stock awards	(325)	$ 12	(337)
Exercise of stock options (in shares)		16
Exercise of stock options	449	$ 5	444
Ending balance (in shares) at Sep. 30, 2017		29,842
Ending Balance at Sep. 30, 2017	453,504	$ 8,951	351,167	115,820	(22,434)
Beginning balance (in shares) at Jun. 30, 2017		29,839
Beginning balance at Jun. 30, 2017	524,695	$ 8,950	341,152	199,348	(24,755)
Net loss	(83,528)			(83,528)
Foreign currency translation adjustment, net of tax	2,605				2,605
Foreign currency hedge, net of tax	(298)				(298)
Change in defined benefit pension plan net actuarial loss, net of tax	14				14
Issuance of convertible debt, net of tax	8,456		8,456
Non-cash compensation	1,582		1,582
Vesting of stock awards (in shares)		3
Vesting of stock awards	(22)	$ 1	(23)
Ending balance (in shares) at Sep. 30, 2017		29,842
Ending Balance at Sep. 30, 2017	453,504	$ 8,951	351,167	115,820	(22,434)
Beginning balance (in shares) at Dec. 31, 2017		29,953
Beginning balance at Dec. 31, 2017	457,468	$ 8,984	352,500	115,780	(19,796)
Adoption of new accounting principle	8,436			8,436
Net loss	(73,177)			(73,177)
Foreign currency translation adjustment, net of tax	(3,311)				(3,311)
Foreign currency hedge, net of tax	348				348
Reclassification of convertible debt embedded derivative, net of tax	37,539		37,539
Non-cash compensation	9,414		9,414
Vesting of stock awards (in shares)		70
Vesting of stock awards	$ (269)	$ 21	(290)
Exercise of stock options (in shares)	0
Ending balance (in shares) at Sep. 30, 2018		30,023
Ending Balance at Sep. 30, 2018	$ 436,448	$ 9,005	399,163	51,039	(22,759)
Beginning balance (in shares) at Jun. 30, 2018		30,019
Beginning balance at Jun. 30, 2018	456,131	$ 9,004	396,800	73,901	(23,574)
Net loss	(22,862)			(22,862)
Foreign currency translation adjustment, net of tax	733				733
Foreign currency hedge, net of tax	82				82
Non-cash compensation	2,408		2,408
Vesting of stock awards (in shares)		4
Vesting of stock awards	(44)	$ 1	(45)
Ending balance (in shares) at Sep. 30, 2018		30,023
Ending Balance at Sep. 30, 2018	$ 436,448	$ 9,005	$ 399,163	$ 51,039	$ (22,759)