Accounts Receivable Grants from Outside Parties (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Nontrade Receivables [Abstract]
Grant proceeds from outside parties			$ 14,881	$ 12,901
Amortization of deferred grants included as offset to depreciation expense	$ 3,315	$ 3,136	$ 6,823	$ 5,603