Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 25,284	$ 22,900	$ 49,256	$ 44,116
Securities available for sale:
Unrealized holding gains on securities	2,569	812	5,476	3,875
Reclassification adjustment for gains realized in net income	0	(772)	0	(728)
Amortization of unrealized holding gains on securities transferred to the held to maturity category	(18)	(18)	(169)	(38)
Total securities	2,551	22	5,307	3,109
Derivative instruments:
Unrealized holding (losses) gains on derivative instruments	(165)	(428)	4	(1,694)
Total derivative instruments	(165)	(428)	4	(1,694)
Defined benefit pension and post-retirement benefit plans:
Amortization of net actuarial loss recognized in net periodic pension cost	56	80	125	152
Total defined benefit pension and post-retirement benefit plans	56	80	125	152
Other comprehensive income (loss), net of tax	2,442	(326)	5,436	1,567
Comprehensive income	$ 27,726	$ 22,574	$ 54,692	$ 45,683