Derivative Instruments - Schedule of settlement of fair value hedges (Details) - Fair value hedges - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Notes Payable And Debt [Member]
Derivative [Line Items]
Cumulative reduction to interest expense	$ 0	$ 20,810
Remaining balance	$ 0	$ 814
Weighted average years remaining to maturity		2 months 12 days
Deposit liabilities
Derivative [Line Items]
Cumulative reduction to interest expense	$ 99,141	$ 90,615
Remaining balance	$ 134,054	$ 142,580
Weighted average years remaining to maturity	22 years 4 months 24 days	24 years