Quarterly Financial Information (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended
Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Selected Quarterly Financial Information [Abstract]
Total revenues	$ 124,837us-gaap_SalesRevenueNet	$ 95,892us-gaap_SalesRevenueNet	$ 32,108us-gaap_SalesRevenueNet	$ 29,810us-gaap_SalesRevenueNet	$ 32,446us-gaap_SalesRevenueNet	$ 29,964us-gaap_SalesRevenueNet	$ 28,124us-gaap_SalesRevenueNet	$ 30,767us-gaap_SalesRevenueNet	$ 282,647us-gaap_SalesRevenueNet	$ 121,301us-gaap_SalesRevenueNet	$ 108,582us-gaap_SalesRevenueNet
Net income	$ 4,361us-gaap_ProfitLoss	$ (2,601)us-gaap_ProfitLoss	$ 4,879us-gaap_ProfitLoss	$ 4,619us-gaap_ProfitLoss	$ 6,347us-gaap_ProfitLoss	$ 4,203us-gaap_ProfitLoss	$ 2,478us-gaap_ProfitLoss	$ 4,539us-gaap_ProfitLoss	$ 11,258us-gaap_ProfitLoss	$ 17,567us-gaap_ProfitLoss	$ 16,331us-gaap_ProfitLoss
Net income per common unit	$ 0.12	$ (0.10)	$ 0.31	$ 0.29	$ 0.40	$ 0.27	$ 0.16	$ 0.29	$ 0.47	$ 1.11	$ 1.04
Net income per diluted common unit	$ 0.12	$ (0.10)	$ 0.30	$ 0.29	$ 0.40	$ 0.26	$ 0.15	$ 0.29	$ 0.47	$ 1.10	$ 1.03

Per unit of ownership amount after tax of income (loss) available to limited partnership (LP) unit-holder and units that would have been outstanding assuming the issuance of limited partner units for dilutive potential units outstanding.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187171-122770

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 4

-Section F

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Per unit of ownership amount after tax of income (loss) available to outstanding limited partnership (LP) unit-holder.

+ References

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The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

-SubTopic 10

-Section 55

-Paragraph 4K

-URI http://asc.fasb.org/extlink&oid=31814832&loc=SL4591552-111686

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

-SubTopic 10

-Section 45

-Paragraph 19

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

-SubTopic 10

-Section 50

-Paragraph 1A

-Subparagraph (a),(c)

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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-Section 55

-Paragraph 4J

-URI http://asc.fasb.org/extlink&oid=31814832&loc=SL4591551-111686

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Total revenue from sale of goods and services rendered during the reporting period, in the normal course of business, reduced by sales returns and allowances, and sales discounts.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 5

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