CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock	Treasury Stock	Shares Held Under Employee Participation Plan	Additional Paid-in Capital	Accumulated Other Comprehensive Income (loss)	Accumulated Earnings
Balance at Dec. 31, 2010	$ 780,827	$ 528	$ (2,467)	$ (777)	$ 488,384	$ 50,759	$ 244,400
Balance (in shares) at Dec. 31, 2010		52,772,000
Increase (Decrease) in Stockholders' Equity
Net income	127,252						127,252
Elimination of treasury stock			2,467		(2,467)
Other comprehensive income (loss)	(19,406)					(19,406)
Stock-based compensation	7,854				7,854
Stock-based compensation (in shares)		322,000
Issuance of restricted shares, net of shares remitted	(4,061)				(4,061)
Issuance of restricted shares, net of shares remitted (in shares)		(76,000)
Shares held under employee participation plan	308			308
Exercise of stock options	1,350	4			1,346
Exercise of stock options (in shares)		71,000
Net tax benefit on exercise of stock-based awards	3,347				3,347
Employee stock purchase plan	3,516				3,516
Employee stock purchase plan (in shares)		94,000
Balance at Dec. 31, 2011	900,987	532	0	(469)	497,919	31,353	371,652
Balance (in shares) at Dec. 31, 2011		53,183,000
Increase (Decrease) in Stockholders' Equity
Net income	129,674						129,674
Other comprehensive income (loss)	18,279					18,279
Stock-based compensation	7,494				7,494
Stock-based compensation (in shares)		168,000
Issuance of restricted shares, net of shares remitted	(2,912)				(2,912)
Issuance of restricted shares, net of shares remitted (in shares)		(48,000)
Issuance of common stock, net of issuance costs	369,520	69			369,451
Issuance of common stock, net of issuance costs (in shares)		6,900,000
Exercise of stock options	288	3			285
Exercise of stock options (in shares)		47,000
Net tax benefit on exercise of stock-based awards	2,546				2,546
Employee stock purchase plan	6,196				6,196
Employee stock purchase plan (in shares)		135,000
Balance at Dec. 31, 2012	1,432,072	604	0	(469)	880,979	49,632	501,326
Balance (in shares) at Dec. 31, 2012		60,385,000
Increase (Decrease) in Stockholders' Equity
Net income	95,566						95,566
Other comprehensive income (loss)	(69,188)					(69,188)
Stock-based compensation	8,946				8,946
Stock-based compensation (in shares)		74,000
Issuance of restricted shares, net of shares remitted	(731)				(731)
Issuance of restricted shares, net of shares remitted (in shares)		(19,000)
Issuance costs related to issuances of common stock	(250)				(250)
Exercise of stock options	400	3			397
Exercise of stock options (in shares)		61,000
Net tax benefit on exercise of stock-based awards	1,399				1,399
Employee stock purchase plan	7,425				7,425
Employee stock purchase plan (in shares)		171,000
Balance at Dec. 31, 2013	$ 1,475,639	$ 607	$ 0	$ (469)	$ 898,165	$ (19,556)	$ 596,892
Balance (in shares) at Dec. 31, 2013		60,672,000