Other Comprehensive Income (Loss) - Reclassification out of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Gains on securities transactions, net	$ 0	$ 0	$ (116)	$ 0
Compensation and employee benefits expense	16,750	15,304	33,275	31,283
Total before tax	17,703	(15,206)	2,113	(30,513)
Income tax benefit	(2,961)	5,934	845	10,946
Net of tax	14,742	(9,272)	2,958	(19,567)
Accumulated other Comprehensive (Loss) Income Components
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total before tax	0	0	789	0
Income tax benefit	0	(2)	(175)	(5)
Net of tax	0	(2)	614	(5)
Accumulated other Comprehensive (Loss) Income Components | Reclassification adjustment for gains included in net income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Gains on securities transactions, net	0	0	116	0
Accumulated other Comprehensive (Loss) Income Components | Reclassification adjustment of actuarial net gain included in net income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Compensation and employee benefits expense	$ 0	$ 0	$ 673	$ 0