Securities Sold Under Agreements to Repurchase (Details) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Contractual maturities of securities sold under repurchase agreements
Total contractual maturities of securities sold under repurchase agreements	$ 1,873,286	$ 1,901,084
Overnight
Contractual maturities of securities sold under repurchase agreements
Total contractual maturities of securities sold under repurchase agreements	41,000
2 to 30 Days
Contractual maturities of securities sold under repurchase agreements
Total contractual maturities of securities sold under repurchase agreements	258,594
31 to 90 Days
Contractual maturities of securities sold under repurchase agreements
Total contractual maturities of securities sold under repurchase agreements	807,005
Over 90 Days
Contractual maturities of securities sold under repurchase agreements
Total contractual maturities of securities sold under repurchase agreements	$ 766,687