Accounts Receivable Grants from Outside Parties (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Receivables [Abstract]
Grant Proceeds From Outside Parties	$ 36,094	$ 41,742	$ 27,980
Amortization of deferred grants included as offset to depreciation expense	$ 13,465	$ 10,691	$ 10,364