Income Taxes (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Dec. 31, 2010
Current:
Federal	$ 69,092	$ 47,799	$ 24,329
State	1,885	1,183	840
Total	70,977	48,982	25,169
Deferred:
Federal	(3,131)	(6,927)	(5,248)
State	0	245	(365)
Total	(3,131)	(6,682)	(5,613)
Total expense:
Federal	65,961	40,872	19,081
State	1,885	1,428	475
Total	$ 67,846	$ 42,300	$ 19,556