Consolidated Statements of Comprehensive Income (Unaudited) - 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	$ 31,964	$ 26,421	$ 102,500	$ 75,677
Securities available for sale:
Unrealized holding (losses) gains on securities	(4,882)	(729)	(15,791)	4,747
Reclassification adjustment for losses (gains) realized in net income	11	(35)	11	(35)
Unrealized holding gains on securities transferred from held to maturity to available for sale	0	8,108	0	8,108
Amortization of unrealized holding gains on securities transferred to the held to maturity category	0	(4)	0	(173)
Total securities	(4,871)	7,340	(15,780)	12,647
Derivative instruments:
Unrealized holding gains on derivative instruments	639	100	1,884	104
Total derivative instruments	639	100	1,884	104
Defined benefit pension and post-retirement benefit plans:
Amortization of net actuarial loss recognized in net periodic pension cost	61	62	184	187
Total defined benefit pension and post-retirement benefit plans	61	62	184	187
Other comprehensive (loss) income, net of tax	(4,171)	7,502	(13,712)	12,938
Comprehensive income	$ 27,793	$ 33,923	$ 88,788	$ 88,615