Offsetting Assets and Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Federal Funds Sold and Securities Borrowed or Purchased under Agreements to Resell [Member] | Assets [Member]
Offsetting Assets [Line Items]
Net amount	$ 1,519,352	$ 1,386,291
Gross amounts recognized	1,519,352	1,386,291
Gross amounts offset in the balance sheet	0	0
Net amounts presented in the balance sheet	1,519,352	1,386,291
Gross amounts not offset in the balance sheet	0	0
Cash Collateral Received/Pledged	0	0
Derivative Financial Instruments, Assets [Member] | Assets [Member]
Offsetting Assets [Line Items]
Net amount	78,857	62,665
Gross amounts recognized	83,978	66,420
Gross amounts offset in the balance sheet	0	0
Net amounts presented in the balance sheet	83,978	66,420
Gross amounts not offset in the balance sheet	(5,121)	(3,755)
Cash Collateral Received/Pledged	0
Assets, Total [Member] | Assets [Member]
Offsetting Assets [Line Items]
Net amount	1,598,209	1,448,956
Gross amounts recognized	1,603,330	1,452,711
Gross amounts offset in the balance sheet	0	0
Net amounts presented in the balance sheet	1,603,330	1,452,711
Gross amounts not offset in the balance sheet	(5,121)	(3,755)
Cash Collateral Received/Pledged	0	0
Federal Funds Purchased and Securities Sold under Agreements to Repurchase [Member] | Other Liabilities [Member]
Offsetting Assets [Line Items]
Net amount	203,597	244,223
Gross amounts recognized	203,597	244,223
Gross amounts offset in the balance sheet	0	0
Net amounts presented in the balance sheet	203,597	244,223
Gross amounts not offset in the balance sheet	0	0
Cash Collateral Received/Pledged	0	0
Derivative Financial Instruments, Liabilities [Member] | Other Liabilities [Member]
Offsetting Assets [Line Items]
Net amount	37,169	30,341
Gross amounts recognized	81,123	66,064
Gross amounts offset in the balance sheet	0	0
Net amounts presented in the balance sheet	81,123	66,064
Gross amounts not offset in the balance sheet	(5,121)	(3,755)
Cash Collateral Received/Pledged	(38,833)	(31,968)
Liabilities, Total [Member] | Other Liabilities [Member]
Offsetting Assets [Line Items]
Net amount	240,766	274,564
Gross amounts recognized	284,720	310,287
Gross amounts offset in the balance sheet	0	0
Net amounts presented in the balance sheet	284,720	310,287
Gross amounts not offset in the balance sheet	(5,121)	(3,755)
Cash Collateral Received/Pledged	$ (38,833)	$ (31,968)