Other Comprehensive Income/Loss - Information About Amounts Reclassified From Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Amounts reclassified from accumulated other comprehensive loss to the consolidated statements of income
Gain on sales of securities	$ 86	$ 72	$ 141
Compensation and benefits	(150,820)	(152,924)	(138,177)
Income before income tax expense	112,257	117,874	122,195
Income tax effect	(40,728)	(29,799)	(26,279)
Net income	71,529	88,075	$ 95,916
Amount reclassified from accumulated other comprehensive income
Amounts reclassified from accumulated other comprehensive loss to the consolidated statements of income
Income before income tax expense	(2,494)	(3,091)
Income tax effect	1,008	1,250
Net income	(1,486)	(1,841)
Amount reclassified from accumulated other comprehensive income | Reclassification adjustment for gain on sales of securities
Amounts reclassified from accumulated other comprehensive loss to the consolidated statements of income
Gain on sales of securities	86	72
Amount reclassified from accumulated other comprehensive income | Reclassification adjustment for net actuarial loss
Amounts reclassified from accumulated other comprehensive loss to the consolidated statements of income
Compensation and benefits	(2,390)	(2,973)
Amount reclassified from accumulated other comprehensive income | Reclassification adjustment for prior service cost
Amounts reclassified from accumulated other comprehensive loss to the consolidated statements of income
Compensation and benefits	$ (190)	$ (190)