Securities - Additional Information (Detail) (USD $)					6 Months Ended
	Jun. 30, 2011 Investment	Dec. 31, 2010 Investment	Jun. 30, 2011 Securities Investment	Dec. 31, 2010 Securities Investment	Jun. 30, 2011 Held to Maturity Debt Securities Excluding Mortgaged Backed Securities
Schedule of Investments [Line Items]
Number of securities held with unrealized loss	41	59
Held-to-Maturity, Amortized Cost	$ 1,966,836,000	$ 2,003,784,000			$ 56,000,000
Held-to-Maturity, Estimated Fair Value	2,014,151,000	2,042,110,000			56,200,000
Maturity of Held-to-maturity Securities, Lower Limit					2017
Maturity of Held-to-maturity Securities, Upper Limit					2018
Accrued interest receivable	53,070,000	55,492,000	7,900,000	8,300,000
Callable Securities Amortized Cost	$ 52,900,000