Dispositions (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	1 Months Ended
Mar. 31, 2015	Feb. 28, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Purchase price of leased vessels	$ 67.4spn_PurchasePriceOfLeasedVessels
Ullswater Vessel [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Repayments of Long-term Capital Lease Obligations		$ 20.9

The cash outflow for the obligation for a lease meeting the criteria for capitalization (with maturities exceeding one year or beyond the operating cycle of the entity, if longer).

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 15

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3291-108585

Name:	us-gaap_RepaymentsOfLongTermCapitalLeaseObligations
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration