New Markets Tax Credit Financing Transaction (Narrative) (Details) - USD ($) $ in Thousands	Mar. 09, 2018	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
New Markets Tax Credit Financing Transaction [Line Items]
New market tax credits recapture percentage	100.00%
New market tax credits period of recapture	7 years
Direct costs incurred in structuring financing transaction		$ 1,489	$ 1,603
Restricted cash		$ 430		$ 6,133
Restricted Cash and Cash Equivalents, Noncurrent, Asset, Statement of Financial Position [Extensible List]		us-gaap:OtherAssetsNoncurrent		us-gaap:OtherAssetsNoncurrent
Other long-term liabilities		$ 3,326	$ 2,835
New Markets Tax Credit (NMTC) Program [Member]
New Markets Tax Credit Financing Transaction [Line Items]
Aggregate principal amount of leverage loan loaned to investment fund	$ 6,700
Leverage loan, due date	2048-03
Direct costs incurred in structuring financing transaction	$ 700
Restricted cash		$ 400
Restricted Cash and Cash Equivalents, Noncurrent, Asset, Statement of Financial Position [Extensible List]		us-gaap:OtherAssetsNoncurrent
Other long-term liabilities		$ 2,800
New Markets Tax Credit (NMTC) Program [Member] | PNC New Markets Investment Partners, LLC [Member]
New Markets Tax Credit Financing Transaction [Line Items]
Capital contributions to investment fund	$ 3,500