Significant Non-Cash Investing Activities (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Other Significant Noncash Transactions [Line Items]
Outstanding receivables from outside parties for the funding of capital expenditures	$ 428,785		$ 375,993
Purchases of property and equipment accrued in accounts payable	12,300	$ 14,900
Accounts receivable - grants from outside parties [Member]
Other Significant Noncash Transactions [Line Items]
Outstanding receivables from outside parties for the funding of capital expenditures	$ 12,178	$ 10,800	$ 10,652