Cash and Cash Equivalents and Fair Value of Financial Instruments - Interest Rate Swaps (Details) - USD ($)	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 7,466,000	$ 54,488,000	$ 47,287,000	$ 82,217,000
Fair value of interest rate swaps	1,200,000	1,245,000
Amounts reclassified into current earnings	$ 0
Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative, notional amount		$ 100,000,000
Derivative, fixed interest rate		0.80%
Fair value of interest rate swaps		$ 1,245,000
Interest Rate Swap | London Interbank Offered Rate (LIBOR)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative, basis spread on variable rate		0.00%