Derivatives - Derivatives Associated with Fixed Income Trading Activities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Customer interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	$ 2,679,166	$ 2,271,448
Assets	93,314	18,744
Liabilities	1,285	27,768
Offsetting upstream interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	2,679,166	2,271,448
Assets	541	4,014
Liabilities	5,509	9,041
Option contracts purchased | Long
Derivative Instruments, Gain (Loss) [Line Items]
Notional	20,000	20,000
Assets	94	25
Liabilities	0	0
Forwards and futures purchased
Derivative Instruments, Gain (Loss) [Line Items]
Notional	10,765,259	4,684,177
Assets	26,191	28,304
Liabilities	8,233	181
Forwards and futures sold
Derivative Instruments, Gain (Loss) [Line Items]
Notional	10,799,031	4,967,454
Assets	9,327	522
Liabilities	$ 25,586	$ 30,055