Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net Income	$ 20,569	$ 12,722	$ 60,076	$ 45,970
Net change in unrealized gains on investment securities available for sale
Net unrealized gains (loss) arising during the period, net of tax expense (benefit) of $761, ($682), $3,498 and $8,668, respectively	1,289	(1,112)	5,802	14,143
Less: reclassification adjustment for net gains on sales realized in net income, net of tax expense of $261, $395, $628 and $718, respectively	(475)	(645)	(1,136)	(1,172)
Net change in unrealized gains (losses) on investment securities available-for-sale	814	(1,757)	4,666	12,971
Net change in securities held to maturity
Amortization of unrealized gain on securities reclassified to held-to-maturity, net of tax expense of $60, $60, $181 and $187, respectively	(99)	(102)	(297)	(305)
Net change in unfunded pension liability
Change in unfunded pension liability related to unrealized (loss) gain, prior service cost and transition obligation, net of tax (benefit) expense of ($15), ($14), ($42) and $266, respectively	(22)	(20)	(67)	436
Net change in cash flow hedge
Net unrealized gain arising during the period, net of tax expense of $26, $38, $118 and $38, respectively	42	61	192	61
Total other comprehensive income (loss)	735	(1,818)	4,494	13,163
Total comprehensive income	$ 21,304	$ 10,904	$ 64,570	$ 59,133