Balance Sheet Offsetting (Assets and liabilities subject to MNA, or repurchase agreements) (Details 2) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Liabilities:
Repurchase Agreements, Gross Amounts of Recognized Liabilities	$ 505,293	$ 523,378
Repurchase Agreements, Gross Amounts Offset in the Statements of Condition	0	0
Repurchase Agreements, Net Amounts of Liabilities Presented in the Statements of Condition	505,293	523,378
Repurchase Agreements, Fair Value of Collateral Pledged	505,293	523,378
Securities Sold under Agreements to Repurchase, Net Amount Offset Against Collateral	0	0
Interest Rate Swap Agreements
Offsetting Assets and Liabilities [Line items]
Net liability positions, aggregate fair value	4,800	5,500
Institutional Counterparties | Interest Rate Swap Agreements
Offsetting Assets and Liabilities [Line items]
Derivative Liability, Fair Value of Collateral	6,000
Assets:
Gross Amounts of Recognized Assets	4,168	5,094
Gross Amounts Offset in the Statements of Condition	0	0
Net Amounts of Assets Presented in the Statements of Condition	4,168	5,094
Netting Adjustments per Master Netting Arrangements	4,168	5,094
Gross Amounts Not Offset in the Statements of Condition - FV of collateral pledged	0	0
Derivative Assets, Net Amount	0	0
Liabilities:
Gross Amounts of Recognized Liabilities	5,998	6,489
Gross Amounts Offset in the Statements of Condition	0	0
Net Amounts of Liabilities Presented in the Statements of Condition	5,998	6,489
Derivative Liability, Netting Adjustments per Master Netting Arrangements	4,168	5,094
Derivative, Collateral, Right to Reclaim Securities	1,830	500
Derivative Liabilities, Net Amount	0	895
Private Institutions
Offsetting Assets and Liabilities [Line items]
Securities Sold under Agreements to Repurchase, Fair Value of Collateral	567,300	599,300
Liabilities:
Repurchase Agreements, Gross Amounts of Recognized Liabilities	500,000	500,000
Repurchase Agreements, Gross Amounts Offset in the Statements of Condition	0	0
Repurchase Agreements, Net Amounts of Liabilities Presented in the Statements of Condition	500,000	500,000
Repurchase Agreements, Fair Value of Collateral Pledged	500,000	500,000
Securities Sold under Agreements to Repurchase, Net Amount Offset Against Collateral	0	0
Government Entities
Offsetting Assets and Liabilities [Line items]
Securities Sold under Agreements to Repurchase, Fair Value of Collateral	7,000	28,900
Liabilities:
Repurchase Agreements, Gross Amounts of Recognized Liabilities	5,293	23,378
Repurchase Agreements, Gross Amounts Offset in the Statements of Condition	0	0
Repurchase Agreements, Net Amounts of Liabilities Presented in the Statements of Condition	5,293	23,378
Repurchase Agreements, Fair Value of Collateral Pledged	5,293	23,378
Securities Sold under Agreements to Repurchase, Net Amount Offset Against Collateral	$ 0	$ 0