Effect of Derivative Instruments on Consolidated Statement of Income and Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Included in Mortgage Banking Income	$ 710	$ 4,504	$ 1,388	$ (10,140)
Treasury Options
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Included in Mortgage Banking Income	11,601	4,390	4,798	7,202
Eurodollar Futures
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Included in Mortgage Banking Income	(1,158)	(1,718)	(1,233)	(1,310)
Forward commitments to buy/sell loans/mortgage-backed securities
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Included in Mortgage Banking Income	$ (9,733)	$ 1,832	$ (2,177)	$ (16,032)