Income Taxes (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Current tax provision (benefit):
Federal			$ (1,600)
State	441	396	451
Total current payable	441	396	(1,149)
Deferred tax provision (benefit):
Federal	31,791	(21,533)	46,994
State	2,507	(1,698)	3,706
Total deferred payable	34,298	(23,231)	50,700
Provision (benefit) for income taxes	$ 34,739	$ (22,835)	$ 49,551