Summary of Income Tax Expense (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Current Income Tax Expense:
Federal			$ 40,697
State	9,797	8,932	7,832
Current Income Tax Expense (Benefit), Total	9,797	8,932	48,529
Deferred Income Tax Expense (Benefit):
Federal	62,015	64,679	15,169
State	(2,202)	(1,201)	(137)
Deferred Income Tax Expense (Benefit), Total	59,813	63,478	15,032
INCOME TAXES	$ 69,610	$ 72,410	$ 63,561