Other Comprehensive Income (Loss) - Reclassification out of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Gains on securities transactions, net	$ 126	$ 116
Compensation and employee benefits expense	2,450	1,550
Income before income tax expense	18,426	15,589
Income tax benefit	(3,507)	(3,805)
Net income	14,919	11,784
Accumulated Other Comprehensive (Loss) Income Components
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income tax expense	290	108
Income tax benefit	(60)	(122)
Net income	230	(14)
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	126	116
Accumulated Other Comprehensive (Loss) Income Components | Reclassification adjustment of actuarial net gain (loss) included in net income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Compensation and employee benefits expense	$ 164	$ (8)