Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Assets and liabilities measured at fair value on a recurring basis
Restricted assets	$ 4,400	$ 5,500
Collateral investments	1,783	3,624
Money Market
Assets and liabilities measured at fair value on a recurring basis
Collateral investments	900	900
Certificate of Deposit
Assets and liabilities measured at fair value on a recurring basis
Collateral investments	900	2,700
Fair value recurring | Money Market
Assets and liabilities measured at fair value on a recurring basis
Restricted assets	4,364	5,497
Collateral investments	905	904
Fair value recurring | Certificate of Deposit
Assets and liabilities measured at fair value on a recurring basis
Collateral investments	878	2,720
Fair value recurring | Quoted Prices in Active Markets for Identical Asset (Level 1) | Money Market
Assets and liabilities measured at fair value on a recurring basis
Restricted assets	4,364	5,497
Collateral investments	905	904
Fair value recurring | Quoted Prices in Active Markets for Identical Asset (Level 1) | Certificate of Deposit
Assets and liabilities measured at fair value on a recurring basis
Collateral investments	$ 878	$ 2,720