CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY AND COMPREHENSIVE INCOME (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock	Additional Paid-in Capital	Treasury Stock	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Balances at Dec. 31, 2008	$ 1,162,509	$ 625	$ 141,283	$ (1,892)	$ 957,200	$ 65,293
Balances (in shares) at Dec. 31, 2008		62,465,572		(176,987)
Comprehensive income, net of tax:
Net income	(99,370)	0	0	0	(99,370)	0
Change in derivative instrument fair value	(35,977)					(35,977)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Reclassification to Earnings, Net of Tax	(67,344)					67,344
Other Comprehensive Income (Loss), Minimum Pension Liability, Adjustment, Net of Tax	74					74
Total comprehensive income	(202,617)
Cash dividends, $ 0.10 per share	(6,247)				(6,247)
Issuance of common stock under Employee Stock Purchase Plan	1,516	1	1,515
Issuance of common stock under Employee Stock Purchase Plan (in shares)		86,308
Issuance of common stock upon vesting of RSUs and settlement of PSUs, net of shares used for tax withholdings, including income tax benefit of RSUs and PSUs	(1,950)	1	(1,951)
Issuance of common stock upon vesting of RSUs and settlement of PSUs, net of shares used for tax withholdings, including income tax benefit of RSUs and PSUs		156,252
Stock Options: Exercised in Period (in shares)		189,740
Sale of common stock, including income tax benefit of stock option exercises	1,594	2	1,592
Stock-based compensation expense, Value	18,765		18,077	688
Stock-based compensation expense, Shares		1,250		50,094
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	196,837	0	0	0	196,837	0
Change in derivative instrument fair value	16,811					16,811
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Reclassification to Earnings, Net of Tax	6,641					(6,641)
Other Comprehensive Income (Loss), Minimum Pension Liability, Adjustment, Net of Tax	(980)					(980)
Total comprehensive income	219,309
Cash dividends, $ 0.10 per share	(6,297)				(6,297)
Issuance of common stock under Employee Stock Purchase Plan	1,670	1	1,669
Issuance of common stock under Employee Stock Purchase Plan (in shares)		52,948
Issuance of common stock upon vesting of RSUs and settlement of PSUs, net of shares used for tax withholdings, including income tax benefit of RSUs and PSUs	(2,093)	1	(2,094)
Issuance of common stock upon vesting of RSUs and settlement of PSUs, net of shares used for tax withholdings, including income tax benefit of RSUs and PSUs		113,103
Stock Options: Exercised in Period (in shares)		346,377
Sale of common stock, including income tax benefit of stock option exercises	5,624	3	5,621
Stock-based compensation expense, Value	26,743		25,962	781
Stock-based compensation expense, Shares		1,250		24,258
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	215,416	0	0	0	215,416	0
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Reclassification to Earnings, Net of Tax	12,997					(12,997)
Other Comprehensive Income (Loss), Minimum Pension Liability, Adjustment, Net of Tax	(1,795)					(1,795)
Total comprehensive income	226,618
Cash dividends, $ 0.10 per share	(6,382)				(6,382)
Issuance of common stock under Employee Stock Purchase Plan	2,300	0	2,300
Issuance of common stock under Employee Stock Purchase Plan (in shares)		41,358
Issuance of common stock upon vesting of RSUs and settlement of PSUs, net of shares used for tax withholdings, including income tax benefit of RSUs and PSUs	(9,973)	3	(9,976)
Issuance of common stock upon vesting of RSUs and settlement of PSUs, net of shares used for tax withholdings, including income tax benefit of RSUs and PSUs		278,773
Stock Options: Exercised in Period (in shares)		412,551
Sale of common stock, including income tax benefit of stock option exercises	5,027	4	5,023
Stock-based compensation expense, Value	26,824		27,945	(1,121)
Stock-based compensation expense, Shares		0		21,568
Balances at Dec. 31, 2011	$ 1,462,940	$ 641	$ 216,966	$ (1,544)	$ 1,251,157	$ (4,280)
Balances (in shares) at Dec. 31, 2011		64,145,482		(81,067)