Derivative Instruments - Schedule of settlement of fair value hedges (Details) (Fair Value Hedging Member, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Notes Payable And Debt
Derivative [Line Items]
Cumulative reduction to interest expense	$ 21,624	$ 18,856
Fair Value Hedge Remaining Balance	0	2,767
Weighted average years to maturity	0 years	0 years 8 months 12 days
Deposit Liabilities
Derivative [Line Items]
Cumulative reduction to interest expense	95,333	37,382
Fair Value Hedge Remaining Balance	$ 137,862	$ 195,814
Weighted average years to maturity	23 years 2 months 12 days	22 years 8 months 12 days