Significant Non-Cash Investing Activities (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Other Significant Noncash Transactions [Line Items]
Outstanding receivables from outside parties for the funding of capital expenditures	$ 401,427,000		$ 363,104,000
Purchases of property and equipment accrued in accounts payable	27,200,000	12,800,000
Accounts receivable - grants from outside parties
Other Significant Noncash Transactions [Line Items]
Outstanding receivables from outside parties for the funding of capital expenditures	$ 20,271,000	$ 23,100,000	$ 32,076,000