Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 61,579	$ 50,603	$ 121,050	$ 97,650
Other comprehensive income (loss), net of tax:
Total available-for-sale and transferred securities	3,200	11,265	975	18,770
Total derivative instruments	651	526	1,810	(426)
Total defined benefit pension and other postretirement benefit plans	1,094	1,095	2,126	2,251
Other comprehensive income, net of tax	4,945	12,886	4,911	20,595
Comprehensive income	$ 66,524	$ 63,489	$ 125,961	$ 118,245