Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 16,220	$ 15,535	$ 46,854	$ 43,985
Securities:
Net change in unrealized holding gains on securities	3,717	866	2,505	4,856
Reclassification adjustment for gains realized in net income	0	(232)	(60)	(232)
Amortization of unrealized holding gains on securities transferred to the held to maturity category	(26)	(38)	(86)	(121)
Total securities	3,691	596	2,359	4,503
Derivative instruments:
Net change in unrealized holding (losses) gains on derivative instruments	(1,075)	42	(881)	(773)
Totals derivative instruments	(1,075)	42	(881)	(773)
Defined benefit pension and post-retirement benefit plans:
Amortization of net actuarial loss recognized in net periodic pension cost	55	47	180	137
Total defined benefit pension and post-retirement benefit plans	55	47	180	137
Other comprehensive income, net of tax	2,671	685	1,658	3,867
Comprehensive income	$ 18,891	$ 16,220	$ 48,512	$ 47,852