Significant Non-Cash Investing Activities (Details) (USD $)	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Other Significant Noncash Transactions [Line Items]
Accounts receivable, gross, current	$ 357,118,000		$ 329,208,000
Purchases of property and equipment accrued in accounts payable but not yet paid	27,800,000	26,700,000
Accounts receivable - grants from outside parties
Other Significant Noncash Transactions [Line Items]
Accounts receivable, gross, current	$ 25,928,000	$ 34,100,000	$ 33,003,000