New Pronouncements - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated other comprehensive loss	$ 294,000	$ (9,856,000)	$ 294,000	$ (9,856,000)	$ (10,893,000)	$ (11,635,000)
Reinvested earnings	250,432,000		250,432,000		$ 244,224,000
Operating earnings	(15,734,000)	(12,315,000)	(42,059,000)	(42,720,000)
Accounting Standards Update 2018-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated other comprehensive loss	1,700,000		1,700,000
Reinvested earnings	1,700,000		1,700,000
Accounting Standards Update 2017-07
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating earnings	11.8	100,000	19,800,000	(200,000)
Other pension benefits (costs)	$ (11,800,000)	$ 100,000	$ (19,800,000)	$ (200,000)