Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Consolidated Statements of Comprehensive Income [Abstract]
Net income	$ 86,136	$ 58,224	$ 44,546
Investment securities available-for-sale:
Change in net unrealized gains (losses) during the period	(52,949)	(4,648)	17,168
Reclassification adjustment for net gains included in income	(1)	(348)	(1,544)
Unamortized premium on available-for-sale securities transferred into held-to-maturity	0	56	389
Defined benefit post-retirement benefits plans:
Change in the net actuarial loss	137	(77)	135
Other comprehensive income (loss), before tax	(52,813)	(5,017)	16,148
Deferred tax benefit (expense) related to other comprehensive income (loss)	20,781	1,974	(6,489)
Other comprehensive income (loss), net of tax	(32,032)	(3,043)	9,659
Total comprehensive income	$ 54,104	$ 55,181	$ 54,205