Subsequent Event (Details) - USD ($) $ / shares in Units, $ in Thousands			6 Months Ended
	Jul. 16, 2015	Apr. 10, 2015	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Subsequent Event [Line Items]
Common units, issued		4,600,000	99,629,218		95,029,218
Sale of Stock, Price Per Share		$ 44.42
Partners' Capital Account, Public Sale of Units Net of Offering Costs		$ 198,000
Senior unsecured notes			$ 1,100,000		$ 1,050,639
Proceeds from issuance of senior unsecured notes, including premium			$ 400,000	$ 350,000
Subsequent Event [Member]
Subsequent Event [Line Items]
Common units, issued	10,350,000
Partners' Capital Account, Public Sale of Units Net of Offering Costs	$ 437,000
Business Acquisition, Transaction Costs	1,500,000
Proceeds from issuance of senior unsecured notes, including premium	728,600
Six Point Seven Five Percentage Senior Unsecured Notes [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Senior unsecured notes	$ 750,000
Debt Instrument, Interest Rate, Stated Percentage	6.75%