Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 167,596	$ 146,920	$ 92,188
Securities available for sale:
Unrealized holding gains (losses) on securities	18,625	(8,315)	(2,218)
Reclassification adjustment for losses (gains) realized in net income	1,872	12	(91)
Unrealized holding gains on securities transferred from held to maturity to available for sale	0	0	8,108
Amortization of unrealized holding gains on securities transferred to the held to maturity category	0	0	(173)
Total securities available for sale	20,497	(8,303)	5,626
Derivative instruments:
Unrealized holding (losses) gains on derivative instruments	(2,217)	365	536
Total derivative instruments	(2,217)	365	536
Defined benefit pension and post-retirement benefit plans:
Net gain arising during the period	68	308	1,028
Amortization of net actuarial loss recognized in net periodic pension cost	312	245	249
Total defined benefit pension and post-retirement benefit plans	380	553	1,277
Other comprehensive income (loss), net of tax	18,660	(7,385)	7,439
Comprehensive income	$ 186,256	$ 139,535	$ 99,627