Condensed 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	$ 98,649	$ 81,682	$ 198,385	$ 161,907
Other comprehensive income (loss), net of tax:
Investment securities available-for-sale	34,409	(9,246)	61,968	(36,670)
Derivative instruments	186	1,680	382	4,202
Defined benefit pension and other postretirement benefit plans	1,056	1,109	2,112	2,063
Other comprehensive income (loss), net of tax	35,651	(6,457)	64,462	(30,405)
Comprehensive income	$ 134,300	$ 75,225	$ 262,847	$ 131,502