Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Consolidated Statements of Comprehensive Income [Abstract]
Net income	$ 121,021	$ 112,566	$ 82,151
Securities available for sale:
Unrealized net holding gains (losses) arising during the period, gross	25,836	(11,985)	(6,915)
Tax effect	(6,459)	2,996	2,845
Unrealized net holding gains (losses) arising during the period, net	19,377	(8,989)	(4,070)
Reclassification adjustment for net (gains) losses in net income, gross	79	6,622	(1,869)
Tax effect	(20)	(1,655)	716
Reclassification adjustment for net (gains) losses in net income, net	59	4,967	(1,153)
Amortization of unrealized net gains for the reclassification of available for sale securities to held to maturity, gross	737	688	875
Tax effect	(184)	(172)	(335)
Amortization of unrealized net gains for the reclassification of available for sale securities to held to maturity, net	553	516	540
Reclassification adjustment for an impairment write-down of equity security, gross	0	0	1,312
Tax effect	0	0	(501)
Reclassification adjustment for an impairment write-down of equity security, net	0	0	811
Total securities available for sale, net	19,989	(3,506)	(3,872)
Cash flow hedges:
Unrealized (losses) gains on derivatives (cash flow hedges), gross	(459)	1,218	901
Tax effect	115	(304)	(350)
Unrealized (losses) gains on derivatives (cash flow hedges), net	(344)	914	551
Reclassification of net unrealized (gains) on cash flow hedges to interest (income), gross	(2,012)	(2,300)	(292)
Tax effect	503	575	113
Reclassification of net unrealized (gains) on cash flow hedges to interest (income), net	(1,509)	(1,725)	(179)
Total cash flow hedges, net	(1,853)	(811)	372
Pension and other benefits:
Amortization of prior service cost and actuarial losses, gross	2,686	1,145	1,852
Tax effect	(672)	(286)	(740)
Amortization of prior service cost and actuarial losses, net	2,014	859	1,112
Decrease (increase) in unrecognized actuarial loss, gross	5,331	(12,457)	2,401
Tax effect	(1,333)	3,038	(570)
Decrease (increase) in unrecognized actuarial loss, net	3,998	(9,419)	1,831
Total pension and other benefits, net	6,012	(8,560)	2,943
Total other comprehensive income (loss)	24,148	(12,877)	(557)
Comprehensive income	$ 145,169	$ 99,689	$ 81,594