Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 22,906	$ 20,609	$ 65,235	$ 62,207
Unrealized gains and losses on securities available for sale:
Net unrealized (losses) gains arising during the period	(1,541)	3,678	8,533	2,460
Reclassification adjustment for losses (gains) included in net income	26	0	(32)	(386)
Total	(1,515)	3,678	8,501	2,074
Unrealized gains (losses) on derivatives	230	(232)	(361)	(232)
Amortization related to post-retirement obligations	141	115	380	227
Total other comprehensive (loss) income	(1,144)	3,561	8,520	2,069
Total comprehensive income	$ 21,762	$ 24,170	$ 73,755	$ 64,276