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	$ 66,274	$ 37,059	$ 127,980	$ 75,868
Change in net unrealized gain (loss) on available-for-sale (AFS) securities, net of tax	(6,501)	3,101	(23,274)	6,479
Accretion of the net unrealized loss on the transfer of AFS securities to held-to-maturity (HTM) securities, net of tax	1	1	2	2
Change in pension plan assets, net of tax	1,052	695	1,785	1,390
Comprehensive income, net of tax	$ 60,826	$ 40,856	$ 106,493	$ 83,739