Fair Value Measurements (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Schedule of assets and liabilities measured at fair value on recurring basis
Interest rate swaps	[1]	$ 69	$ 158
Money market mutual funds
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	[2]	7,318	21,848
United States treasuries
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	[2]	1,001
Certificates of deposit
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	[2]		3,864
Level 1
Schedule of assets and liabilities measured at fair value on recurring basis
Interest rate swaps	[1]	0	0
Level 1 | Money market mutual funds
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	[2]	7,318	21,848
Level 1 | United States treasuries
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	[2]	1,001
Level 1 | Certificates of deposit
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	[2]		3,864
Level 2
Schedule of assets and liabilities measured at fair value on recurring basis
Interest rate swaps	[1]	69	158
Level 2 | Money market mutual funds
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	[2]	0	0
Level 2 | United States treasuries
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	[2]	0
Level 2 | Certificates of deposit
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	[2]		0
Level 3
Schedule of assets and liabilities measured at fair value on recurring basis
Interest rate swaps	[1]	0	0
Level 3 | Money market mutual funds
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	[2]	0	0
Level 3 | United States treasuries
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	[2]	$ 0
Level 3 | Certificates of deposit
Schedule of assets and liabilities measured at fair value on recurring basis
Assets measured at fair value	[2]		$ 0

[1] The valuations of the interest rate swaps intended to mitigate the Company’s interest rate risk are determined with the assistance of a third-party financial institution using widely accepted valuation techniques, including discounted cash flow analysis on the expected cash flows of each instrument. This analysis utilizes observable market-based inputs, including interest rate curves and interest rate volatility, and reflects the contractual terms of these instruments, including the period to maturity.

[2] Market approach—prices and other relevant information generated by market transactions involving identical or comparable assets.