Derivative Instruments (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Mar. 31, 2016
Derivative [Line Items]
Loss on early extinguishment of debt	$ 1,533	$ 0	$ 0
Cash flow hedge gain (loss) to be reclassified within 12 months	271
Remaining unamortized deferred gain (loss) balance of all previously terminated cash flow hedges	(597)	(1,100)
Remaining deferred (gain) loss balance on all previously terminated fair value hedges	4,000	7,600
Deferred gain balance on terminated fair value hedges expected to be reclassified from long-term debt	1,800
Collateral pledge to collateralize derivative liabilities	65,900
Deferred gains of hedges reclassified into earnings	3,100	3,100	$ 3,200
Deferred gains of hedges reclassified into loss on extinguishment of debt	495
Federal Funds Sold, Counterparty with CCC [Member]
Derivative [Line Items]
Collateral pledge to collateralize derivative liabilities	13,700
Fixed Rate Residential Mortgage [Member]
Derivative [Line Items]
Commitments to fund fixed-rate mortgage loans	88,800	73,400
Unrealized gain on fair value of fixed-rate mortgage loans to customers	175	606
Sale of outstanding commitments	95,000	113,000
Unrealized loss on mortgage loans	924	(1,700)
Visa USA [Member]
Derivative [Line Items]
Derivative, fair value	1,400
Interest Rate Swap [Member] | Customer Position [Member]
Derivative [Line Items]
Notional amount of interest rate swap contracts	1,280,000	$ 184,800
Scenario, Forecast [Member]
Derivative [Line Items]
Deferred gain balance on terminated fair value hedges expected to be reclassified from loss on extinguishment of debt				$ 1,300
Reclassification out of Accumulated Other Comprehensive Income [Member]
Derivative [Line Items]
Loss on early extinguishment of debt	$ (196)