Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 21,356	$ 21,796	$ 42,329	$ 41,598
Unrealized gains and losses on securities available for sale:
Net unrealized gains (losses) arising during the period	2,979	(4,929)	10,073	(1,218)
Reclassification adjustment for gains included in net income	0	(385)	(57)	(386)
Total	2,979	(5,314)	10,016	(1,604)
Unrealized losses on derivatives	(170)	0	(591)	0
Amortization related to post-retirement obligations	140	116	239	112
Total other comprehensive income (loss)	2,949	(5,198)	9,664	(1,492)
Total comprehensive income	$ 24,305	$ 16,598	$ 51,993	$ 40,106