Derivatives (Narrative) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2016 USD ($) agreement	Mar. 31, 2015 USD ($)
Derivative [Line Items]
Ineffective portion of change in derivative fair value	$ 0
Derivative income reflected in income statement	(100)	$ (100)
Impact to interest income from cash flow hedges	300	$ 400
Aggregate fair value of derivatives in a net liability position	(31,900)
Collateral obligations for derivative counterparties	$ 33,100
Interest Rate Swaps [Member]
Derivative [Line Items]
Number of interest rate swap agreements | agreement	5
Interest Rate Swaps [Member] | $300 Million Swap Agreement [Member]
Derivative [Line Items]
Notional amount of derivatives	$ 300,000
Swap agreement expiration date	Jan. 01, 2017
Interest Rate Swaps [Member] | $200 Million Swap Agreement [Member]
Derivative [Line Items]
Notional amount of derivatives	$ 200,000
Swap agreement expiration date	Jun. 01, 2017
Interest Rate Swaps [Member] | $100 Million Swap Agreement [Member]
Derivative [Line Items]
Number of interest rate swap agreements | agreement	3
Notional amount of derivatives	$ 100,000
Interest Rate Swaps [Member] | Date One [Member] | $100 Million Swap Agreement [Member]
Derivative [Line Items]
Swap agreement expiration date	Apr. 01, 2018
Interest Rate Swaps [Member] | Date Two [Member] | $100 Million Swap Agreement [Member]
Derivative [Line Items]
Swap agreement expiration date	Apr. 01, 2019
Interest Rate Swaps [Member] | Date Three [Member] | $100 Million Swap Agreement [Member]
Derivative [Line Items]
Swap agreement expiration date	Apr. 01, 2020