Employee Benefits - Components of Net Periodic Pension Cost and Other Changes in Plan Assets and Benefit Obligation Recognized in Other Comprehensive Income (Loss) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Components of Net Periodic Pension Cost
Service cost—benefits earned during the period	$ 0	$ 0	$ 463,000
Interest cost on projected benefit obligation	3,882,000	4,100,000	4,296,000
Expected return on plan assets	(6,266,000)	(6,313,000)	(5,780,000)
Amortization of prior service credit	0	0	(11,000)
Recognized net actuarial loss	2,134,000	1,866,000	2,345,000
Curtailment gain	0	0	(1,017,000)
Net Periodic Pension Expense	(250,000)	(347,000)	296,000
Other Changes in Plan Assets and Benefit Obligation Recognized in Other Comprehensive Income (Loss)
Net actuarial (gain) loss	(3,271,000)	3,678,000	(6,018,000)
Recognized net actuarial loss	(2,134,000)	(1,866,000)	(2,345,000)
Recognized prior service credit	0	0	1,029,000
Total (Before Tax Effects)	(5,405,000)	1,812,000	(7,334,000)
Total Recognized in Net Benefit Cost and Other Comprehensive (Loss)/Income (Before Tax Effects)	$ (5,655,000)	$ 1,465,000	$ (7,038,000)