Consolidated Statements of Stockholders' Equity (USD $) In Thousands, unless otherwise specified	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Retained Earnings [Member]	Other Comprehensive (Loss) Income [Member]
Beginning balance at Dec. 31, 2008	$ 903,219	$ 409	$ 711,444	$ 0	$ 234,751	$ (43,385)
COMPREHENSIVE INCOME:
Net income (loss)	(23)				(23)
Unrealized gain (loss) on natural gas derivatives, net of deferred income taxes	867					867
Unrealized gain on interest rate derivatives, net of deferred income taxes	1,777					1,777
Minimum pension liability, net of deferred income taxes	7,314					7,314
Comprehensive income	9,935
Exercise of stock options	145		145
Net tax expense related to stock-based compensation	(3,126)		(3,126)
Employee stock plan purchases	415	1	414
Issuance of stock to employees	6		6
Restricted stock units surrendered	(112)		(112)
Restricted stock shares surrendered	(61)		(61)
Issuance of common stock	125,297	60	125,237
Issuance of common stock warrants	43,740		43,740
Issuance of convertible notes, including equity-related issuance costs	66,107		66,107
Purchase of convertible note hedge	(76,680)		(76,680)
Purchase of Company's common stock to fund a supplemental employee retirement plan	(525)		4,074	(4,599)
Stock-based compensation expense	10,324		10,324
Ending balance at Dec. 31, 2009	1,078,684	470	881,512	(4,599)	234,728	(33,427)
COMPREHENSIVE INCOME:
Net income (loss)	(89,128)				(89,128)
Unrealized gain (loss) on natural gas derivatives, net of deferred income taxes	(145)					(145)
Unrealized gain on interest rate derivatives, net of deferred income taxes	8,621					8,621
Minimum pension liability, net of deferred income taxes	(3,138)					(3,138)
Comprehensive income	(83,790)
Exercise of stock options	25,712	10	25,702
Net tax expense related to stock-based compensation	(254)		(254)
Employee stock plan purchases	354		354
Issuance of stock to employees	9		9
Restricted stock units surrendered	(1,278)	1	(1,279)
Restricted stock shares surrendered	(34)		(34)
Stock-based compensation expense	10,349		10,349
Ending balance at Dec. 31, 2010	1,029,752	481	916,359	(4,599)	145,600	(28,089)
COMPREHENSIVE INCOME:
Net income (loss)	10,177				10,177
Unrealized gain (loss) on natural gas derivatives, net of deferred income taxes	145					145
Unrealized gain on interest rate derivatives, net of deferred income taxes	7,860					7,860
Minimum pension liability, net of deferred income taxes	(15,947)					(15,947)
Comprehensive income	2,235
Exercise of stock options	4,459	2	4,457
Net tax expense related to stock-based compensation	(524)		(524)
Employee stock plan purchases	369		369
Issuance of stock to employees	13		13
Restricted stock units surrendered	(904)	1	(905)
Restricted stock shares surrendered	(18)		(18)
Stock-based compensation expense	10,153		10,153
Ending balance at Dec. 31, 2011	$ 1,045,535	$ 484	$ 929,904	$ (4,599)	$ 155,777	$ (36,031)