Condensed Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Retained Earnings (Accumulated Deficit)	Accumulated Other Comprehensive Loss	Total
Balance at Dec. 31, 2017	$ 619,235	$ 38,450	$ 91,816		$ 749,501
Balance (in shares) at Dec. 31, 2017	73,871,424
Changes in Shareholders' Equity
Net loss			(450)		(450)
Stock issued upon stock option exercises	$ 2,461	(552)			1,909
Stock issued upon stock option exercises (in shares)	200,677
Share-based compensation		3,161			3,161
Stock issued upon vesting of restricted stock units	$ 157	(157)
Stock issued upon vesting of restricted stock units (in shares)	10,705
Balance at Mar. 31, 2018	$ 621,853	40,902	91,240		753,995
Balance (in shares) at Mar. 31, 2018	74,082,806
Balance at Dec. 31, 2017	$ 619,235	38,450	91,816		749,501
Balance (in shares) at Dec. 31, 2017	73,871,424
Changes in Shareholders' Equity
Net loss					(4,414)
Other comprehensive loss, net of tax					(962)
Balance at Jun. 30, 2018	$ 625,354	45,804	87,276	$ (962)	757,472
Balance (in shares) at Jun. 30, 2018	74,282,135
Changes in Shareholders' Equity
Cumulative effect adjustment | ASU 2014-09			(126)		(126)
Balance at Mar. 31, 2018	$ 621,853	40,902	91,240		753,995
Balance (in shares) at Mar. 31, 2018	74,082,806
Changes in Shareholders' Equity
Net loss			(3,964)		(3,964)
Stock issued upon stock option exercises	$ 1,831	(389)			1,442
Stock issued upon stock option exercises (in shares)	129,722
Share-based compensation		6,961			6,961
Stock issued upon vesting of restricted stock units	$ 1,109	(1,109)
Stock issued upon vesting of restricted stock units (in shares)	47,683
Restricted stock award activity	$ 561	(561)
Restricted stock award activity (in shares)	21,924
Other comprehensive loss, net of tax				(962)	(962)
Balance at Jun. 30, 2018	$ 625,354	45,804	87,276	(962)	757,472
Balance (in shares) at Jun. 30, 2018	74,282,135
Balance at Dec. 31, 2018	$ 629,411	50,544	(210,579)	(4,292)	$ 465,084
Balance (in shares) at Dec. 31, 2018	74,474,677				74,474,677
Changes in Shareholders' Equity
Net loss			(14,301)		$ (14,301)
Share-based compensation		3,572			3,572
Stock issued upon vesting of restricted stock units	$ 4,766	(4,766)
Stock issued upon vesting of restricted stock units (in shares)	244,948
Restricted stock award activity	$ 37	(37)
Restricted stock award activity (in shares)	(5,929)
Other comprehensive loss, net of tax				(2,127)	(2,127)
Balance at Mar. 31, 2019	$ 634,214	49,313	(219,228)	(6,419)	457,880
Balance (in shares) at Mar. 31, 2019	74,713,696
Balance at Dec. 31, 2018	$ 629,411	50,544	(210,579)	(4,292)	$ 465,084
Balance (in shares) at Dec. 31, 2018	74,474,677				74,474,677
Changes in Shareholders' Equity
Net loss					$ (173,763)
Other comprehensive loss, net of tax					(5,485)
Balance at Jun. 30, 2019	$ 636,331	51,597	(378,690)	(9,777)	$ 299,461
Balance (in shares) at Jun. 30, 2019	74,993,966				74,993,966
Changes in Shareholders' Equity
Cumulative effect adjustment | ASU 2016-02			5,652		$ 5,652
Balance at Mar. 31, 2019	$ 634,214	49,313	(219,228)	(6,419)	457,880
Balance (in shares) at Mar. 31, 2019	74,713,696
Changes in Shareholders' Equity
Net loss			(159,462)		(159,462)
Stock issued upon stock option exercises	$ 148	(30)			118
Stock issued upon stock option exercises (in shares)	27,313
Share-based compensation		4,283			4,283
Stock issued upon vesting of restricted stock units	$ 1,544	(1,544)
Stock issued upon vesting of restricted stock units (in shares)	65,988
Restricted stock award activity	$ 425	(425)
Restricted stock award activity (in shares)	186,969
Other comprehensive loss, net of tax				(3,358)	(3,358)
Balance at Jun. 30, 2019	$ 636,331	$ 51,597	$ (378,690)	$ (9,777)	$ 299,461
Balance (in shares) at Jun. 30, 2019	74,993,966				74,993,966