Capital (Details 4) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Basic Earnings:
Net income attributable to SLGOP common unitholders	$ 20,677	$ 8,299	$ 106,461	$ 26,144	$ 3,491	$ 7,248	$ 538,383	$ 82,739	$ 161,581	$ 631,861	$ 275,400
Diluted Earnings:
Income attributable to SLGOP common unitholders									$ 161,581	$ 631,861	$ 275,400
Basic Earnings:
Units attributable to common unitholders (in shares)									92,526	85,747	79,422
Effect of Dilutive Securities:
Stock-based compensation plans (in shares)									347	497	339
Diluted Units (in shares)									92,873	86,244	79,761
Common units excluded from the diluted shares outstanding									627,000	680,000	804,800