Employee Benefit Plans - Summary of Information About Plan Assets And Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plans [Member]
Changes in plan assets and benefit obligations recognized in Other Comprehensive Income [Abstract]
Net actuarial loss	$ 109	$ 10,912	$ 5,695
Amortization of net loss	(3,040)	(2,256)	(2,095)
Settlement charges	(1,409)		(3,345)
Total recognized in other comprehensive (income) loss	(4,340)	8,656	255
Net periodic benefit cost	3,798	1,538	5,364
Total recognized in net periodic benefit cost and other comprehensive loss	(542)	10,194	5,619
SERP [Member]
Changes in plan assets and benefit obligations recognized in Other Comprehensive Income [Abstract]
Net actuarial loss	11,024	7,395	566
Amortization of net loss	(3,171)	(2,471)	(2,354)
Settlement charges	(2,006)	(2,514)	(1,121)
Total recognized in other comprehensive (income) loss	5,847	2,410	(2,909)
Net periodic benefit cost	7,081	6,504	5,478
Total recognized in net periodic benefit cost and other comprehensive loss	$ 12,928	$ 8,914	$ 2,569