Offsetting Assets and Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 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	$ 1,404,246	$ 1,386,291
Gross amounts recognized	1,704,246	1,386,291
Gross amounts offset in the balance sheet	(300,000)	0
Net amounts presented in the balance sheet	1,404,246	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	57,738	62,665
Gross amounts recognized	63,962	66,420
Gross amounts offset in the balance sheet	0	0
Net amounts presented in the balance sheet	63,962	66,420
Gross amounts not offset in the balance sheet	(6,224)	$ (3,755)
Cash Collateral Received/Pledged	0
Assets, Total [Member] | Assets [Member]
Offsetting Assets [Line Items]
Net amount	1,461,984	$ 1,448,956
Gross amounts recognized	1,768,208	1,452,711
Gross amounts offset in the balance sheet	(300,000)	0
Net amounts presented in the balance sheet	1,468,208	1,452,711
Gross amounts not offset in the balance sheet	(6,224)	(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	227,124	244,223
Gross amounts recognized	527,124	244,223
Gross amounts offset in the balance sheet	(300,000)	0
Net amounts presented in the balance sheet	227,124	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	26,930	30,341
Gross amounts recognized	60,245	66,064
Gross amounts offset in the balance sheet	0	0
Net amounts presented in the balance sheet	60,245	66,064
Gross amounts not offset in the balance sheet	(6,224)	(3,755)
Cash Collateral Received/Pledged	(27,091)	(31,968)
Liabilities, Total [Member] | Other Liabilities [Member]
Offsetting Assets [Line Items]
Net amount	254,054	274,564
Gross amounts recognized	587,369	310,287
Gross amounts offset in the balance sheet	(300,000)	0
Net amounts presented in the balance sheet	287,369	310,287
Gross amounts not offset in the balance sheet	(6,224)	(3,755)
Cash Collateral Received/Pledged	$ (27,091)	$ (31,968)