Employee Benefit Plans - Narrative (Details)	3 Months Ended	6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Anticipated cash contributions to pension plan in remaining fiscal year	$ 0	$ 0
Estimated liability to withdraw from plan	3,340,000	3,340,000
Estimated liability to withdraw from plan, current	240,000	240,000
Estimated liability to withdraw from plan, noncurrent	3,100,000	3,100,000
Pension and Other Postretirement Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Interest cost	1,225,000	2,450,000
Expected return on assets	$ 1,971,000	$ 3,942,000