Other Comprehensive Income/Loss (Amounts Reclassified From Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Amounts reclassified from accumulated other comprehensive loss to the consolidated statements of income
Reclassification adjustment for gain on sales of securities included in net income, before tax amount	$ 0	$ (141)	$ (72)	$ (141)
Reclassification adjustment for net actuarial loss	743	228	2,229	685
Reclassification adjustment for prior service cost	48	47	143	142
Income before income tax expense	29,436	29,064	89,904	92,617
Income tax effect	(10,530)	(10,256)	(20,260)	(19,960)
Net income	18,906	18,808	69,644	72,657
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	(791)	(134)	(2,300)	(686)
Income tax effect	320	47	930	242
Net income	(471)	(87)	(1,370)	(444)
Net unrealized (loss) gain on securities available-for-sale | 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 included in net income, before tax amount	0	141	72
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	(743)	(228)	(2,229)	(685)
Reclassification adjustment for prior service cost	$ (48)	$ (47)	$ (143)	$ (142)