Condensed Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Restricted Stock Units Restricted Stock Units	Additional Paid-in Capital	Exchangeable Shares of Subsidiary	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of the change in accounting principle related to revenue recognition						$ 0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance						111,798
Beginning Balance at Dec. 31, 2016		$ 414	$ 85,907	$ 734,728	$ 1,958	111,798	$ (32,398)	$ (611,224)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock issued		24		65,231
Restricted stock units recognized, net of forfeitures			40,597
Restricted stock units delivered			(45,992)
Tax benefit from the delivery of restricted stock units				847
Exchangeable shares of subsidiary delivered					0
Dividends						(47,552)
Net income (loss)						(26,651)
Currency translation adjustment, net of tax							10,176
Repurchased								(79,561)
Ending Balance at Dec. 31, 2017	$ 208,302	438	80,512	800,806	1,958	37,595	(22,222)	(690,785)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of the change in accounting principle related to revenue recognition						(7,645)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance						29,950
Stock issued		10		39,443
Restricted stock units recognized, net of forfeitures			15,243
Restricted stock units delivered			(39,912)
Tax benefit from the delivery of restricted stock units				0
Exchangeable shares of subsidiary delivered					0
Dividends						(3,117)
Net income (loss)	16,881					16,881
Currency translation adjustment, net of tax	(7,239)						(7,239)
Repurchased								(119,401)
Ending Balance at Jun. 30, 2018	$ 102,565	$ 448	$ 55,843	$ 840,249	$ 1,958	$ 43,714	$ (29,461)	$ (810,186)