Derivatives - Derivatives Associated with Fixed Income Trading Activities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Customer interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	$ 2,390,963	$ 2,271,448
Assets	63,951	18,744
Liabilities	3,084	27,768
Offsetting upstream interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	2,390,963	2,271,448
Assets	2,666	4,014
Liabilities	5,638	9,041
Option contracts purchased | Long
Derivative Instruments, Gain (Loss) [Line Items]
Notional	52,500	20,000
Assets	111	25
Liabilities	0	0
Call Option | Long
Derivative Instruments, Gain (Loss) [Line Items]
Notional	10,000
Assets	0
Liabilities	16
Forwards and futures purchased
Derivative Instruments, Gain (Loss) [Line Items]
Notional	9,322,784	4,684,177
Assets	36,693	28,304
Liabilities	800	181
Forwards and futures sold
Derivative Instruments, Gain (Loss) [Line Items]
Notional	9,767,188	4,967,454
Assets	1,441	522
Liabilities	$ 37,191	$ 30,055