Income Tax (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2010
Current
Federal taxes									$ 36,109	$ 28,979	$ 23,750
State taxes									8,614	6,501	5,043
Foreign taxes									73
Total current taxes									44,796	35,480	28,793
Deferred
Federal taxes									(3,571)	(2,168)	(768)
State taxes									(502)	(502)	(186)
Foreign taxes									(73)
Total deferred taxes									(4,146)	(2,670)	(954)
Provision for income taxes	$ 8,521	$ 11,247	$ 11,002	$ 9,880	$ 9,929	$ 8,305	$ 7,587	$ 6,989	$ 40,650	$ 32,810	$ 27,839