Derivative Instruments - Schedule of settlement of fair value hedges (Details) - Fair value hedging - Deposit liabilities - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Derivative [Line Items]
Cumulative reduction to interest expense	$ 124,255	$ 122,118
Remaining balance	$ 108,940	$ 111,077
Weighted average years remaining to maturity	18 years 3 months	18 years 8 months 12 days