CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 16,251	$ 14,989
Securities available for sale and transferred securities:
Change in net unrealized holding (losses) gains on available for sale securities during the period	(37,783)	4,885
Unrealized net gain on securities transferred from held to maturity to available for sale under the transition guidance enumerated in ASU 2017-12	11,881	0
Change in net unrealized losses on securities transferred from held to maturity to available for sale	401	0
Reclassification adjustment for net loss on equity investments, reclassed to retained earnings with adoption of ASU 2016-01	107	0
Reclassification adjustment for amortization related to available for sale and held to maturity debt securities	138	488
Reclassification adjustment for net loss (gain) on sale of available for sale securities, included in net income	827	(322)
Derivatives:
Change in net unrealized gain (loss) on effective cash flow hedge interest rate swap derivatives	4,245	(80)
Change in net unrealized gains on interest rate swap derivatives terminated during the period	0	273
Reclassification adjustment from other comprehensive income related to derivatives designated as cash flow hedge	(127)	370
Pension plans:
Amortization of net actuarial loss and prior service credit, included in net periodic benefit cost	473	389
Other comprehensive (loss) income, before tax	(19,838)	6,003
Income tax benefit (expense) related to items of other comprehensive income (loss)	4,166	(2,101)
Other comprehensive (loss) income, net of tax	(15,672)	3,902
Comprehensive income	$ 579	$ 18,891