Derivatives (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
Ineffective portion of change in derivative fair value	$ 0
Aggregate fair value of derivatives in a net liability position	22,100
Collateral obligations for derivative counterparties	19,100
Cash Flow Hedge [Member]
Derivative [Line Items]
Impact to interest income from cash flow hedges	2,300	$ 2,100	$ 300
Derivatives Designated as Hedging Instruments [Member]
Derivative [Line Items]
Notional amount of derivatives	1,100,000	500,000
Interest Rate Swaps [Member]
Derivative [Line Items]
Derivative income reflected in income statement	5,200	2,700	$ 1,600
Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedge [Member]
Derivative [Line Items]
Notional amount of derivatives	1,100,000	$ 500,000
Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedge [Member] | Swap Agreement 1, Expires 2017 [Member]
Derivative [Line Items]
Notional amount of derivatives	$ 500,000
Derivative maturity expiration year	2017
Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedge [Member] | Swap Agreement 2, Expires 2018 [Member]
Derivative [Line Items]
Notional amount of derivatives	$ 200,000
Derivative maturity expiration year	2018
Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedge [Member] | Swap Agreement 3, Expires 2019 [Member]
Derivative [Line Items]
Notional amount of derivatives	$ 200,000
Derivative maturity expiration year	2019
Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedge [Member] | Swap Agreement 4, Expires 2020 [Member]
Derivative [Line Items]
Notional amount of derivatives	$ 200,000
Derivative maturity expiration year	2020