Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 10,895	$ 7,792	$ 29,470	$ 23,749
Available-for-sale investment securities:
Gross unrealized holding (loss) gain arising in the period	(236)	(4,068)	5,448	14,681
Related tax benefit (expense)	83	1,424	(1,906)	(5,139)
Less: reclassification adjustment for net gain (loss) included in net income	1,861	(1)	2,219	862
Related tax expense	(652)	0	(777)	(302)
Net effect on other comprehensive (loss) income	(1,362)	(2,643)	2,100	8,982
Defined benefit plans:
Net loss arising during the period	(1)	0	(1)	0
Amortization of unrecognized loss and service cost on benefit plans	25	21	72	66
Related tax expense	(9)	(9)	(25)	(22)
Net effect on other comprehensive income	15	12	46	44
Cash flow hedges:
Net (loss) gain arising during the period	(63)	68	(832)	(184)
Related tax benefit (expense)	22	(24)	291	64
Net effect on other comprehensive (loss) income	(41)	44	(541)	(120)
Total other comprehensive (loss) income, net of tax expense	(1,388)	(2,587)	1,605	8,906
Total comprehensive income	$ 9,507	$ 5,205	$ 31,075	$ 32,655