Securities Sold Under Agreements to Repurchase (Details ) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Securities sold under repurchase agreements
Total contractual maturities of securities sold under repurchase agreements	$ 1,065,653	$ 1,925,998
2 to 30 Days
Securities sold under repurchase agreements
Total contractual maturities of securities sold under repurchase agreements	201,100
31 to 90 Days
Securities sold under repurchase agreements
Total contractual maturities of securities sold under repurchase agreements	160,911
Over 90 Days
Securities sold under repurchase agreements
Total contractual maturities of securities sold under repurchase agreements	$ 703,642