Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 12,725	$ 10,895	$ 32,358	$ 29,470
Available-for-sale investment securities:
Gross unrealized holding (loss) gain arising during the period	(5,813)	(236)	(18,587)	5,448
Related tax benefit (expense)	1,221	83	3,904	(1,906)
Less: reclassification adjustment for net gain (loss) included in net income	0	1,861	(146)	2,219
Related tax (expense) benefit	0	(652)	31	(777)
Amounts reclassified out of accumulated other comprehensive loss per ASU 2016-01 (a)	0	0	(5,020)	0
Related tax benefit	0	0	1,054	0
Net effect on other comprehensive (loss) income	(4,592)	(1,362)	(18,534)	2,100
Defined benefit plans:
Net gain (loss) arising during the period	1,177	(1)	1,177	(1)
Related tax expense	(247)	0	(247)	0
Amortization of unrecognized loss and service cost on benefit plans	28	25	80	72
Related tax expense	(6)	(9)	(17)	(25)
Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), before Tax	176	0	176	0
Other Comprehensive Income (Loss), Defined Benefit Plan, Adjustment for Settlement or Curtailment Gain (Loss), Tax	(37)	0	(37)	0
Net effect on other comprehensive income	1,091	15	1,132	46
Cash flow hedges:
Net gain (loss) arising during the period	651	(63)	2,566	(832)
Related tax (expense) benefit	(137)	22	(539)	291
Net effect on other comprehensive income (loss)	514	(41)	2,027	(541)
Total other comprehensive (loss) income, net of tax expense	(2,987)	(1,388)	(15,375)	1,605
Total comprehensive income	$ 9,738	$ 9,507	$ 16,983	$ 31,075