Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 17,029	$ 17,828
Unrealized gains and losses on securities available for sale:
Net unrealized gains (losses) arising during the period	3,719	(1,620)
Reclassification adjustment for losses (gains) included in net income	207	(302)
Total	3,926	(1,922)
Amortization related to post-retirement obligations	(48)	259
Total other comprehensive income (loss)	3,878	(1,663)
Total comprehensive income	$ 20,907	$ 16,165