Pension Benefits and Other Postretirement Benefit Plans (Additional Information) (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) plan	Sep. 30, 2017 USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Number of qualified noncontributory defined benefit plans | plan			2
Anticipated payment for defined benefit pensions	$ 25,000		$ 25,347	$ 372
Bear Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Required employer contribution		$ 200		$ 400