Accounts Receivable Grants from Outside Parties (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Receivables [Abstract]
Grant proceeds received from outside parties	$ 41,700	$ 28,000	$ 33,900
Amortization of deferred grants included as offset to depreciation expense	$ 10,691	$ 10,364	$ 9,343