Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 27,913	$ 23,508
Unrealized gains and losses on available for sale debt securities:
Net unrealized (losses) gains arising during the period	(9,639)	771
Reclassification adjustment for gains included in net income	0	0
Total	(9,639)	771
Unrealized gains on derivatives	530	55
Amortization related to post-retirement obligations	62	32
Total other comprehensive (loss) income	(9,047)	858
Total comprehensive income	$ 18,866	$ 24,366