Derivatives - Gains/(Losses) on Derivatives Associated with Interest Rate Risk Management Activities (Details) - Hedging Instruments And Hedged Items - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Customer Interest Rate Contracts Hedging | Customer interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(Losses) related to interest rate derivatives	$ (10,620)	$ (180)	$ (39,803)	$ 643
Customer Interest Rate Contracts Hedging | Offsetting upstream interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(Losses) related to interest rate derivatives	10,620	180	39,803	(643)
Debt Hedging | Interest rate swaps
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(Losses) related to interest rate derivatives	(246)	(966)	(8,386)	(1,958)
Debt Hedging | Term borrowings
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(Losses) related to term borrowings	$ 240	$ 941	$ 8,310	$ 1,870