CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY AND COMPREHENSIVE INCOME (USD $) In Thousands, except Share data	Total	Common Stock	Additional Paid-in Capital	Treasury Stock	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Comprehensive Income
Balances at Dec. 31, 2009	$ 973,570	$ 629	$ 160,516	$ (1,204)	$ 851,583	$ (37,954)
Balances (in shares) at Dec. 31, 2009		62,899,122		(126,893)
Comprehensive income, net of tax:
Net income	144,246				144,246		144,246
Change in derivative instrument fair value	53,765					53,765	53,765
Reclassification to earnings	(782)					(782)	(782)
Minimum pension liability adjustment	4					4	4
Total comprehensive income	197,233						197,233
Cash dividends, $ 0.05 per share	(3,144)				(3,144)
Issuance of common stock under Employee Stock Purchase Plan	799		799
Issuance of common stock under Employee Stock Purchase Plan (in shares)		27,456
Issuance of common stock upon vesting of RSUs, net of shares used for tax withholdings, including income tax benefit (cost) of RSUs	(544)	1	(545)
Issuance of common stock upon vesting of RSUs, net of shares used for tax withholdings, including income tax benefit (cost) of RSUs (in shares)		34,588
Sale of common stock, including income tax benefit of stock option exercises	3,055	1	3,054
Sale of common stock, including income tax benefit of stock option exercises (in shares)		148,902
Stock-based compensation expense	11,864		11,149	715
Stock-based compensation expense (in shares)				24,258
Balances at Jun. 30, 2010	1,182,833	631	174,973	(489)	992,685	15,033
Balances (in shares) at Jun. 30, 2010		63,110,068		(102,635)
Balances at Dec. 31, 2010	1,218,526	634	191,674	(423)	1,042,123	(15,482)
Balances (in shares) at Dec. 31, 2010		63,412,800		(102,635)
Comprehensive income, net of tax:
Net income	106,030				106,030		106,030
Reclassification to earnings	4,878					4,878	4,878
Total comprehensive income	110,908						110,908
Cash dividends, $ 0.05 per share	(3,181)				(3,181)
Issuance of common stock under Employee Stock Purchase Plan	1,122	1	1,121
Issuance of common stock under Employee Stock Purchase Plan (in shares)		22,373
Issuance of common stock upon vesting of RSUs, net of shares used for tax withholdings, including income tax benefit (cost) of RSUs	(644)		(644)
Issuance of common stock upon vesting of RSUs, net of shares used for tax withholdings, including income tax benefit (cost) of RSUs (in shares)		18,836
Sale of common stock, including income tax benefit of stock option exercises	10,598	3	10,595
Sale of common stock, including income tax benefit of stock option exercises (in shares)		310,412
Stock-based compensation expense	11,837		12,958	(1,121)
Stock-based compensation expense (in shares)				21,568
Balances at Jun. 30, 2011	$ 1,349,166	$ 638	$ 215,704	$ (1,544)	$ 1,144,972	$ (10,604)
Balances (in shares) at Jun. 30, 2011		63,764,421		(81,067)