Other Comprehensive Income/Loss (Details 3) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Amounts reclassified from accumulated other comprehensive loss to the consolidated statements of income
Reclassification adjustment for gain on sales of securities		$ (2,057)		$ (2,057)
Reclassification adjustment for net actuarial loss	249	838	457	1,805
Reclassification adjustment for prior service cost	48	53	95	106
Income before income tax expense	33,768	24,560	63,553	46,193
Income tax effect	(11,468)	(8,895)	(9,704)	(16,676)
Net income	22,300	15,665	53,849	29,517
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	(297)	1,166	(552)	146
Income tax effect	105	(411)	195	(52)
Net income	(192)	755	(357)	94
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		2,057		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	(249)	(838)	(457)	(1,805)
Reclassification adjustment for prior service cost	$ (48)	$ (53)	$ (95)	$ (106)