Derivatives - Derivatives Associated with Fixed Income Trading Activities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Customer interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	$ 2,279,361	$ 2,271,448
Assets	30,632	18,744
Liabilities	14,245	27,768
Offsetting upstream interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	2,279,361	2,271,448
Assets	5,056	4,014
Liabilities	4,834	9,041
Option contracts purchased | Long
Derivative Instruments, Gain (Loss) [Line Items]
Notional	72,500	20,000
Assets	103	25
Liabilities	0	0
Forwards and futures purchased
Derivative Instruments, Gain (Loss) [Line Items]
Notional	7,983,000	4,684,177
Assets	31,733	28,304
Liabilities	4,404	181
Forwards and futures sold
Derivative Instruments, Gain (Loss) [Line Items]
Notional	8,373,739	4,967,454
Assets	5,243	522
Liabilities	$ 32,284	$ 30,055