Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 20,484	$ 18,594	$ 59,469	$ 45,505
Other comprehensive income (loss), net of tax
Net change in fair value of securities available for sale	(816)	1,211	5,119	544
Net change in fair value of cash flow hedges	674	132	653	596
Net change in other comprehensive income for defined benefit postretirement plans	59	110	180	309
Total other comprehensive income (loss)	(83)	1,453	5,952	1,449
Total comprehensive income	$ 20,401	$ 20,047	$ 65,421	$ 46,954