Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 76,648	$ 64,960	$ 59,845
Other comprehensive income (loss), net of tax
Net change in fair value of securities available for sale	(1,133)	(2,083)	5,412
Net change in fair value of cash flow hedges	2,170	1,199	2,256
Net change in other comprehensive income for defined benefit postretirement plans	78	564	(2,366)
Total other comprehensive income (loss)	1,115	(320)	5,302
Total comprehensive income	$ 77,763	$ 64,640	$ 65,147