CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 12,865	$ 11,762	$ 37,776	$ 32,305
Securities available for sale and transferred securities:
Net unrealized holding (losses) gains on available for sale securities during the period	(10,960)	13,446	33,031	6,722
Change in net unrealized loss on securities transferred to held to maturity	0	0	0	1,329
Reclassification adjustment for amortization of unrealized losses on securities transferred to held to maturity	16	220	160	746
Reclassification adjustment for net gain on sale of available for sale securities, included in net income	(2,343)	(875)	(5,512)	(3,456)
Derivatives:
Change in net unrealized loss on effective cash flow hedge interest rate swap derivatives	1,070	0	(5,125)	0
Reclassification adjustment for net loss on interest rate swap derivatives, included in net income	521	0	1,338	0
Pension plans:
Amortization of net actuarial loss, included in net periodic benefit cost	458	691	1,371	1,836
Amortization of prior service credit, included in net periodic benefit cost	(10)	(4)	(6)	(12)
Other comprehensive (loss) income, before tax	(11,248)	13,478	25,257	7,165
Income tax benefit (expense) related to items of other comprehensive income (loss)	3,937	(4,718)	(8,840)	(2,508)
Other comprehensive (loss) income, net of tax	(7,311)	8,760	16,417	4,657
Comprehensive income	$ 5,554	$ 20,522	$ 54,193	$ 36,962