CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 38,935	$ 20,569	$ 105,025	$ 60,076
Net change in unrealized (loss) gains on investment securities available for sale
Net unrealized (loss) gains arising during the period, net of tax (benefit) expense of ($1,846), $761, ($6,958) and $3,498, respectively	(6,042)	1,289	(22,370)	5,802
Less: reclassification adjustment for net gains on sales realized in net income, net of tax expense of $0, $261, $5, and $628, respectively	0	(475)	(16)	(1,136)
Net change in unrealized gains (losses) on investment securities available-for-sale	(6,042)	814	(22,386)	4,666
Net change in securities held to maturity
Amortization of unrealized gain on securities reclassified to held-to-maturity, net of tax expense (benefit) of $36, $60, $109 and $181, respectively	(107)	(99)	(343)	(297)
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 $(9), ($15), $1, and ($42), respectively	(30)	(22)	(1)	(67)
Net change in cash flow hedge
Net unrealized (loss) gain arising during the period, net of tax expense (benefit) of ($75), $26, ($391) and $118 respectively	(109)	42	(1,119)	192
Total other comprehensive (loss) income	(6,288)	735	(23,849)	4,494
Total comprehensive income	$ 32,647	$ 21,304	$ 81,176	$ 64,570