Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 17,451	$ 14,746	$ 26,910	$ 28,129
Other comprehensive income (loss), net of tax
Net change in fair value of securities available for sale	(2,228)	2,395	(667)	4,312
Net change in fair value of cash flow hedges	382	1,005	464	1,507
Net change in other comprehensive income for defined benefit postretirement plans	123	(39)	199	(78)
Total other comprehensive income (loss)	(1,723)	3,361	(4)	5,741
Total comprehensive income	$ 15,728	$ 18,107	$ 26,906	$ 33,870