New Pronouncements - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating earnings	$ 16,351	$ 16,840	$ 26,325	$ 30,405
Accounting Standards Update 2017-07
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating earnings	(8,000)	200	(8,000)	300
Other pension benefits (costs)	$ 8,000	$ 200	$ 8,000	$ 300