Other Comprehensive Income (Loss) - Reclassification out of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Gains on securities transactions, net	$ 0	$ 2,099	$ (116)	$ 2,099
Compensation and employee benefits expense	16,654	16,700	49,928	47,983
Total before tax	(17,783)	(1,708)	(15,669)	(32,220)
Income tax benefit	6,956	194	7,800	11,140
Net of tax	(10,827)	(1,514)	(7,869)	(21,080)
Accumulated other Comprehensive (Loss) Income Components
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total before tax	0	0	779	1,998
Income tax benefit	3	25	(170)	(619)
Net of tax	3	25	609	1,379
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	$ 663	$ 1,998