Other Comprehensive (Loss) Income (Reclassifications Out of AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Compensation and employee benefits	$ 27,546	$ 27,328	$ 83,398	$ 81,086
Income tax expense	(8,575)	(11,969)	(19,504)	(30,788)
Net income	35,468	26,575	82,624	74,466
Reclassification adjustment [Member] | Post-retirement obligations [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Compensation and employee benefits	100	61	300	183
Income tax expense	(25)	(25)	(78)	(78)
Net income	$ 75	$ 36	$ 222	$ 105