Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 46,625	$ 36,710	$ 91,735	$ 70,536
Securities available for sale:
Unrealized holding gains (losses) on securities	9,393	(3,000)	20,710	(10,909)
Reclassification adjustment for losses (gains) realized in net income	6	0	(4)	0
Total securities	9,399	(3,000)	20,706	(10,909)
Derivative instruments:
Unrealized holding (losses) gains on derivative instruments	(1,541)	387	(2,456)	1,245
Total derivative instruments	(1,541)	387	(2,456)	1,245
Defined benefit pension and post-retirement benefit plans:
Amortization of net actuarial loss recognized in net periodic pension cost	102	57	156	123
Total defined benefit pension and post-retirement benefit plans	102	57	156	123
Other comprehensive income (loss), net of tax	7,960	(2,556)	18,406	(9,541)
Comprehensive income	$ 54,585	$ 34,154	$ 110,141	$ 60,995