Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 146,920	$ 92,188	$ 90,930
Securities available for sale:
Unrealized holding losses on securities	(8,315)	(2,218)	(6,206)
Reclassification adjustment for losses (gains) realized in net income	12	(91)	(727)
Unrealized holding gains on securities transferred from held to maturity to available for sale	0	8,108	0
Amortization of unrealized holding gains on securities transferred to the held to maturity category	0	(173)	(61)
Total securities available for sale	(8,303)	5,626	(6,994)
Derivative instruments:
Unrealized holding gains on derivative instruments	365	536	527
Total derivative instruments	365	536	527
Defined benefit pension and post-retirement benefit plans:
Net gain arising during the period	308	1,028	31
Amortization of net actuarial loss recognized in net periodic pension cost	245	249	302
Reclassification adjustment for net settlement gain realized in net income	0	0	(235)
Total defined benefit pension and post-retirement benefit plans	553	1,277	98
Other comprehensive (loss) income, net of tax	(7,385)	7,439	(6,369)
Comprehensive income	$ 139,535	$ 99,627	$ 84,561