Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent			21.00%	34.00%
Net deferred income tax liabilities	$ 28,498		$ 28,498			$ 28,763
Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration	8,000		8,000			8,000
Deferred Tax Liabilities, Other						20,900
Deferred Tax Liabilities, Goodwill and Intangible Assets	21,100		21,100
Unrecognized Tax Benefits	1,400		1,400			1,400
Income Tax Examination, Penalties and Interest Expense	0	$ 100	200	$ 400
Income Tax Examination, Penalties and Interest Accrued					$ 1,000	$ 900
Deferred Tax Liabilities, Regulatory Assets and Liabilities	$ 100		$ 100