Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Consolidated Statements of Comprehensive Income (unaudited) [Abstract]
Net income	$ 24,713	$ 30,555	$ 35,081	$ 59,682
Securities available for sale:
Unrealized net holding gains arising during the period, gross	6,433	13,391	27,772	24,427
Tax effect	(1,608)	(3,348)	(6,943)	(6,107)
Unrealized net holding gains arising during the period, net	4,825	10,043	20,829	18,320
Reclassification adjustment for net (gains) losses in net income, gross	0	0	(3)	99
Tax effect	0	0	1	(25)
Reclassification adjustment for net (gains) losses in net income, net	0	0	(2)	74
Amortization of unrealized net gains for the reclassification of available for sale securities to held to maturity, gross	165	199	338	366
Tax effect	(42)	(50)	(85)	(92)
Amortization of unrealized net gains for the reclassification of available for sale securities to held to maturity, net	123	149	253	274
Total securities available for sale, net	4,948	10,192	21,080	18,668
Cash flow hedges:
Unrealized (losses) on derivatives (cash flow hedges), gross	(19)	(314)	(274)	(484)
Tax effect	5	78	69	121
Unrealized (losses) on derivatives (cash flow hedges), net	(14)	(236)	(205)	(363)
Reclassification of net unrealized losses (gains) on cash flow hedges to interest (income), gross	81	(738)	91	(1,537)
Tax effect	(20)	185	(23)	385
Reclassification of net unrealized losses (gains) on cash flow hedges to interest (income), net	61	(553)	68	(1,152)
Total cash flow hedges, net	47	(789)	(137)	(1,515)
Pension and other benefits:
Amortization of prior service cost and actuarial losses, gross	381	657	762	1,313
Tax effect	(96)	(164)	(191)	(328)
Amortization of prior service cost and actuarial losses, net	285	493	571	985
Total pension and other benefits, net	285	493	571	985
Total other comprehensive income	5,280	9,896	21,514	18,138
Comprehensive income	$ 29,993	$ 40,451	$ 56,595	$ 77,820