Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Consolidated Statements of Comprehensive Income (Unaudited) [Abstract]
Net income	$ 30,555	$ 28,121	$ 59,682	$ 54,107
Securities available for sale:
Unrealized net holding gains (losses) arising during the period, gross	13,391	(5,353)	24,427	(20,807)
Tax effect	(3,348)	1,338	(6,107)	5,202
Unrealized net holding gains (losses) arising during the period, net	10,043	(4,015)	18,320	(15,605)
Reclassification adjustment for net losses in net income, gross	0	0	99	0
Tax effect	0	0	(25)	0
Reclassification adjustment for net losses in net income, net	0	0	74	0
Amortization of unrealized net gains for the reclassification of available for sale securities to held to maturity, gross	199	177	366	365
Tax effect	(50)	(44)	(92)	(91)
Amortization of unrealized net gains for the reclassification of available for sale securities to held to maturity, net	149	133	274	274
Total securities available for sale, net	10,192	(3,882)	18,668	(15,331)
Cash flow hedges:
Unrealized (losses) gains on derivatives (cash flow hedges), gross	(314)	424	(484)	1,472
Tax effect	78	(106)	121	(368)
Unrealized (losses) gains on derivatives (cash flow hedges), net	(236)	318	(363)	1,104
Reclassification of net unrealized (gains) on cash flow hedges to interest (income), gross	(738)	(540)	(1,537)	(899)
Tax effect	185	135	385	225
Reclassification of net unrealized (gains) on cash flow hedges to interest (income), net	(553)	(405)	(1,152)	(674)
Total cash flow hedges, net	(789)	(87)	(1,515)	430
Pension and other benefits:
Amortization of prior service cost and actuarial losses, gross	657	295	1,313	590
Tax effect	(164)	(74)	(328)	(148)
Amortization of prior service cost and actuarial losses, net	493	221	985	442
Total pension and other benefits, net	493	221	985	442
Total other comprehensive income (loss)	9,896	(3,748)	18,138	(14,459)
Comprehensive income	$ 40,451	$ 24,373	$ 77,820	$ 39,648