Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Consolidated Statements of Comprehensive Income
Net income	$ 99,473	$ 75,437	$ 49,219
Unrealized gains (losses) on securities:
Unrealized holding gains (losses) arising during period	(5,142)	17,843	(23,069)
Tax effect	1,961	(6,804)	8,732
Reclassification adjustment for gains (losses) included in net income	489	2
Tax effect	(187)	(1)
Net of tax amount	(2,879)	11,040	(14,337)
Unrealized gains (losses) on derivative financial instruments qualifying as cash flow hedges:
Unrealized holding gains (losses) arising during period	(168)	(252)	283
Tax effect	64	96	(108)
Reclassification adjustment for losses included in interest expense	305	310	307
Tax effect	(116)	(118)	(117)
Net of tax amount	85	36	365
Change in pension and retiree medical plan obligation:
Change in pension and retiree medical plan obligation during period	(2,229)	(3,727)	5,804
Tax effect	897	1,526	(2,249)
Reclassification adjustment for actuarial (gains) losses included in salaries and employee benefits	1,021	761	482
Tax effect	(389)	(290)	(164)
Net of tax amount	(700)	(1,730)	3,873
Other comprehensive income (loss), net of tax	(3,494)	9,346	(10,099)
Total comprehensive income	$ 95,979	$ 84,783	$ 39,120