Statements of Condensed Consolidated Comprehensive (Loss) Income (Unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2018
Statement of Comprehensive Income [Abstract]
Other post-retirement benefits liability adjustments, tax		$ 10		$ 20
Other post-retirement benefits liability adjustments, tax	$ 24	$ 26	$ 48	$ 52
Accounting Standards Update [Extensible List]					us-gaap:AccountingStandardsUpdate201802Member