Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 18,808	$ 16,924	$ 72,657	$ 46,441
Net unrealized (loss) gain on securities available-for-sale:
Net unrealized holding (loss) gain on securities arising during the period	(420)	(1,286)	7,272	(7,889)
Reclassification adjustment for gain on sales of securities included in net income	(91)		(91)	(1,332)
Net unrealized (loss) gain on securities available-for-sale	(511)	(1,286)	7,181	(9,221)
Reclassification adjustment for net actuarial loss on pension plans and other postretirement benefits included in net income	147	585	443	1,754
Reclassification adjustment for prior service cost on pension plans and other postretirement benefits included in net income	31	34	92	103
Total other comprehensive (loss) income, net of tax	(333)	(667)	7,716	(7,364)
Comprehensive income	$ 18,475	$ 16,257	$ 80,373	$ 39,077