Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Consolidated Statements of Comprehensive Income [Abstract]
Net income	$ 112,566	$ 82,151	$ 78,409
Securities available for sale:
Unrealized net holding (losses) arising during the period, gross	(11,985)	(6,915)	(8,618)
Tax effect	2,996	2,845	3,353
Unrealized net holding (losses) arising during the period, net	(8,989)	(4,070)	(5,265)
Reclassification adjustment for net losses (gains) in net income, gross	6,622	(1,869)	644
Tax effect	(1,655)	716	(251)
Reclassification adjustment for net losses (gains) in net income, net	4,967	(1,153)	393
Amortization of unrealized net gains for the reclassification of available for sale securities to held to maturity, gross	688	875	1,094
Tax effect	(172)	(335)	(426)
Amortization of unrealized net gains for the reclassification of available for sale securities to held to maturity, net	516	540	668
Reclassification adjustment for an impairment write-down of equity security, gross	0	1,312	0
Tax effect	0	(501)	0
Reclassification adjustment for an impairment write-down of equity security, net	0	811	0
Total securities available for sale, net	(3,506)	(3,872)	(4,204)
Cash flow hedges:
Unrealized gains on derivatives (cash flow hedges), gross	1,218	901	2,832
Tax effect	(304)	(350)	(1,102)
Unrealized gains on derivatives (cash flow hedges), net	914	551	1,730
Reclassification of net unrealized (gains) losses on cash flow hedges to interest (income) expense, gross	(2,300)	(292)	69
Tax effect	575	113	(27)
Reclassification of net unrealized (gains) losses on cash flow hedges to interest (income) expense, net	(1,725)	(179)	42
Total cash flow hedges, net	(811)	372	1,772
Pension and other benefits:
Amortization of prior service cost and actuarial gains, gross	1,145	1,852	2,370
Tax effect	(286)	(740)	(949)
Amortization of prior service cost and actuarial gains, net	859	1,112	1,421
(Increase) decrease in unrecognized actuarial loss, gross	(12,457)	2,401	3,154
Tax effect	3,038	(570)	(1,245)
(Increase) decrease in unrecognized actuarial loss, net	(9,419)	1,831	1,909
Total pension and other benefits, net	(8,560)	2,943	3,330
Total other comprehensive (loss) income	(12,877)	(557)	898
Comprehensive income	$ 99,689	$ 81,594	$ 79,307