Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 36,710	$ 25,284	$ 70,536	$ 49,256
Securities available for sale:
Unrealized holding (losses) gains on securities	(3,000)	2,569	(10,909)	5,476
Amortization of unrealized holding gains on securities transferred to the held to maturity category	0	(18)	0	(169)
Total securities	(3,000)	2,551	(10,909)	5,307
Derivative instruments:
Unrealized holding gains (losses) on derivative instruments	387	(165)	1,245	4
Total derivative instruments	387	(165)	1,245	4
Defined benefit pension and post-retirement benefit plans:
Amortization of net actuarial loss recognized in net periodic pension cost	57	56	123	125
Total defined benefit pension and post-retirement benefit plans	57	56	123	125
Other comprehensive (loss) income, net of tax	(2,556)	2,442	(9,541)	5,436
Comprehensive income	$ 34,154	$ 27,726	$ 60,995	$ 54,692