Other Comprehensive Income/Loss (Details 3) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Amounts reclassified from accumulated other comprehensive loss to the consolidated statements of income
Reclassification adjustment for gain on sales of securities	$ (141)		$ (141)	$ (2,057)
Reclassification adjustment for net actuarial loss	228	903	685	2,708
Reclassification adjustment for prior service cost	47	53	142	159
Income before income tax expense	29,064	26,438	92,617	72,631
Income tax effect	(10,256)	(9,514)	(19,960)	(26,190)
Net income	18,808	16,924	72,657	46,441
Amount Reclassified from Accumulated Other Comprehensive Loss
Amounts reclassified from accumulated other comprehensive loss to the consolidated statements of income
Income before income tax expense	(134)	(956)	(686)	(810)
Income tax effect	47	337	242	285
Net income	(87)	(619)	(444)	(525)
Gain on sales of securities | Amount Reclassified from Accumulated Other Comprehensive Loss
Amounts reclassified from accumulated other comprehensive loss to the consolidated statements of income
Reclassification adjustment for gain on sales of securities	141		141	2,057
Compensation and benefits | Amount Reclassified from Accumulated Other Comprehensive Loss
Amounts reclassified from accumulated other comprehensive loss to the consolidated statements of income
Reclassification adjustment for net actuarial loss	(228)	(903)	(685)	(2,708)
Reclassification adjustment for prior service cost	$ (47)	$ (53)	$ (142)	$ (159)