Consolidated Statements of Comprehensive Income - 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	$ 15,394	$ 14,853	$ 30,634	$ 28,450
Securities:
Net change in unrealized holding (losses) gains on securities	(3,836)	1,206	(1,212)	3,990
Reclassification adjustment for gains realized in net income	(60)	0	(60)	0
Amortization of unrealized holding gains on securities transferred to the held to maturity category	(28)	(39)	(60)	(83)
Total securities	(3,924)	1,167	(1,332)	3,907
Derivative instruments:
Net change in unrealized holding gains (losses) on derivative instruments	863	(396)	194	(815)
Totals derivative instruments	863	(396)	194	(815)
Defined benefit pension and post-retirement benefit plans:
Amortization of net actuarial loss recognized in net periodic pension cost	68	45	125	90
Total defined benefit pension and post-retirement benefit plans	68	45	125	90
Other comprehensive (loss) income, net of tax	(2,993)	816	(1,013)	3,182
Comprehensive income	$ 12,401	$ 15,669	$ 29,621	$ 31,632