Financial Instruments and Fair Value Measurements - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Expected amount to receive upon maturity of note after payment of note and any other liabilities	$ 20,000,000.0
Retained interest investments	10,635,000	$ 10,246,000
Other than temporary impairment losses, investments	0	0
Senior Notes held by special purpose entity	176,310,000	176,094,000
Assets, fair value, nonrecurring	$ 0	0
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Retained interest, effective interest rate	3.70%
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Retained interest, effective interest rate	11.80%
Special Purpose Entities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Expected amount to receive upon maturity of note after payment of note and any other liabilities	$ 16,900,000
Retained interest investments	$ 10,600,000	$ 10,200,000
Promissory notes maturity period	15 years
Special Purpose Entities | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes maturity year	2022
Special Purpose Entities | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes maturity year	2024
Short-term bond | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment term	0 years
Short-term bond | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment term	3 years