Financial Instruments and Fair Value Measurements - Additional information (Details) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2008	Dec. 31, 2014	Dec. 31, 2007
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total debt	$ 68,277,000		$ 68,277,000			$ 63,804,000
Retained interest promissory note receivable	20,000,000		20,000,000		$ 15,200,000
Notes, maturity period					15 years
Retained Interest
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other than Temporary Impairment Losses, Investments	0	$ 0	0	$ 0
Carrying Value | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Retained Interest, Fair Value Disclosure	$ 10,078,000		$ 10,078,000			$ 9,932,000
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Note maturity year					2022
Retained interest, effective interest rate			3.70%
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Note maturity year					2024
Retained interest, effective interest rate			11.60%
Defeased Debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total debt							$ 29,300,000