Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Consolidated Statements of Comprehensive Income
Net income	$ 186,483	$ 178,871	$ 87,554
Unrealized gains (losses) on available for sale securities:
Unrealized holding gains (losses) arising during period	36,211	(17,322)	(3,486)
Tax effect	(7,966)	3,843	1,329
Reclassification adjustment for (gains) losses included in net income	2,655	655	(668)
Tax effect	(584)	(145)	255
Net of tax amount	30,316	(12,969)	(2,570)
Unrealized gains (losses) on derivative financial instruments qualifying as cash flow hedges:
Unrealized holding gains (losses) arising during period	(13,394)	42	(22)
Tax effect	2,947	(9)	9
Reclassification adjustment for gains (losses) included in interest expense	(349)	155	275
Tax effect	77	(34)	(105)
Net of tax amount	(10,719)	154	157
Change in pension plan obligation:
Change in pension and retiree medical plan obligation during period	25	490	(589)
Tax effect	(5)	(108)	224
Reclassification adjustment for changes included in net income	8,053	1,187	908
Tax effect	(1,772)	(261)	(346)
Net of tax amount	6,301	1,308	197
Other comprehensive income (loss), net of tax	25,898	(11,507)	(2,216)
Comprehensive income	$ 212,381	$ 167,364	$ 85,338