CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings
Beginning Balance at Dec. 31, 2015	$ 751,443	$ 917	$ (367,121)	$ 1,019,670	$ (47,902)	$ 145,879
Beginning Balance, shares (in shares) at Dec. 31, 2015		91,714,000
Beginning Balance, Treasury Stock, shares (in shares) at Dec. 31, 2015			(17,830,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	74,564					74,564
Other comprehensive income (loss), net of tax	(9,252)				(9,252)
Treasury shares retirement	0	$ (178)	$ 367,121	(366,943)
Treasury shares retirement (in shares)		(17,830,000)	(17,830,000)
Settlement of convertible notes	0	$ 29		(29)
Settlement of convertible notes (in shares)		2,946,000
Exercise of convertible note hedge	0		$ (123,051)	123,051
Exercise of convertible note hedge (in shares)			(2,946,000)
Issuance of common stock through employee stock purchase plan	391	$ 1		390
Issuance of common stock through employee stock purchase plan (in shares)		12,000
Issuance of common stock for vesting of share-based awards, net of shares withheld for taxes	5,211	$ 8		5,203
Issuance of common stock for vesting of share-based awards, net of shares withheld for taxes (in shares)		824,000
Share-based compensation	17,310			17,310
Ending Balance at Dec. 31, 2016	839,667	$ 777	$ (123,051)	798,652	(57,154)	220,443
Ending Balance, shares (in shares) at Dec. 31, 2016		77,666,000
Ending Balance, Treasury Stock, shares (in shares) at Dec. 31, 2016			(2,946,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	64,743					64,743
Other comprehensive income (loss), net of tax	33,347				33,347
Issuance of common stock through employee stock purchase plan	509			509
Issuance of common stock through employee stock purchase plan (in shares)		12,000
Issuance of common stock for vesting of share-based awards, net of shares withheld for taxes	2,138	$ 8	$ 1,407	723
Issuance of common stock for vesting of share-based awards, net of shares withheld for taxes (in shares)		788,000	19,000
Exercise of warrants		$ 28		(28)
Exercise of warrants (in shares)		2,840,000
Share-based compensation	21,902			21,902
Ending Balance at Dec. 31, 2017	$ 962,306	$ 813	$ (121,644)	821,758	(23,807)	285,186
Ending Balance, shares (in shares) at Dec. 31, 2017		81,306,000
Ending Balance, Treasury Stock, shares (in shares) at Dec. 31, 2017	(2,912,000)		(2,927,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 60,801					60,801
Other comprehensive income (loss), net of tax	(21,636)				(21,636)
Issuance of common stock through employee stock purchase plan	553			553
Issuance of common stock for vesting of share-based awards, net of shares withheld for taxes	1,085	$ 4	$ 1,029	52
Issuance of common stock for vesting of share-based awards, net of shares withheld for taxes (in shares)		700,000	46,000
Equity offering	349,589	$ 60		349,529
Equity Offering (in shares)		6,038,000
Share-based compensation	20,712	$ 3		20,709
Ending Balance at Dec. 31, 2018	$ 1,375,796	$ 880	$ (120,615)	$ 1,192,601	$ (45,443)	$ 348,373
Ending Balance, shares (in shares) at Dec. 31, 2018		88,044,000
Ending Balance, Treasury Stock, shares (in shares) at Dec. 31, 2018	(2,881,000)		(2,881,000)