Significant Non-Cash Investing Activities (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Other Significant Noncash Transactions [Line Items]
Outstanding receivables from outside parties for the funding of capital expenditures	$ 450,676		$ 430,210
Purchases of property and equipment accrued in accounts payable	16,100	$ 12,300
Accounts receivable - grants from outside parties [Member]
Other Significant Noncash Transactions [Line Items]
Outstanding receivables from outside parties for the funding of capital expenditures	$ 14,610	$ 12,200	$ 17,734