Debt, Credit Facility (Details) - USD ($)			12 Months Ended
	Apr. 21, 2017	Jun. 08, 2012	Dec. 31, 2017	Dec. 31, 2016
Line of Credit Facility [Line Items]
Long term debt outstanding			$ 145,959,000	$ 210,343,000
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Total availability under the revolving credit facility			$ 92,600,000
Prior Credit Agreement [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Initiation date			Jun. 08, 2012
Maximum borrowing capacity		$ 125,000,000
Prior Credit Agreement [Member] | Revolving Credit Facility [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Unused commitment fee percentage		0.20%
Prior Credit Agreement [Member] | Revolving Credit Facility [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Unused commitment fee percentage		0.50%
Prior Credit Agreement [Member] | Revolving Credit Facility [Member] | LIBOR [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Variable rate basis		0.00%
Margin rate		1.75%
Prior Credit Agreement [Member] | Revolving Credit Facility [Member] | LIBOR [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Margin rate		3.00%
Prior Credit Agreement [Member] | Revolving Credit Facility [Member] | One-Month LIBOR [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate		1.00%
Prior Credit Agreement [Member] | Revolving Credit Facility [Member] | Federal Funds Rate [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate		0.50%
Prior Credit Agreement [Member] | Revolving Credit Facility [Member] | Base Rate [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Margin rate		0.75%
Prior Credit Agreement [Member] | Revolving Credit Facility [Member] | Base Rate [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Margin rate		2.00%
Prior Credit Agreement [Member] | Swingline Sub Facility [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity		$ 20,000,000
Prior Credit Agreement [Member] | Letters of Credit Sub Facility [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity		75,000,000
Prior Credit Agreement [Member] | Term Loan Facility A [Member]
Line of Credit Facility [Line Items]
Debt instrument, face amount		200,000,000
Prior Credit Agreement [Member] | Uncommitted Incremental Accordion Facility [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity		$ 100,000,000
Credit Agreement [Member]
Line of Credit Facility [Line Items]
Initiation date			Apr. 21, 2017
Maturity date			Apr. 21, 2022
Credit Agreement [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Unused commitment fee percentage	0.20%
Credit Agreement [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Unused commitment fee percentage	0.50%
Credit Agreement [Member] | Federal Funds Rate [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.50%
Credit Agreement [Member] | LIBOR [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Variable rate basis	0.00%
Margin rate	1.50%
Credit Agreement [Member] | LIBOR [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Margin rate	2.75%
Credit Agreement [Member] | One-Month LIBOR [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.00%
Credit Agreement [Member] | Base Rate [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Margin rate	0.50%
Credit Agreement [Member] | Base Rate [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Margin rate	1.75%
Credit Agreement [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 100,000,000
Credit Agreement [Member] | Swingline Sub Facility [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity	25,000,000
Credit Agreement [Member] | Letters of Credit Sub Facility [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity	75,000,000
Credit Agreement [Member] | Term Loan Facility A [Member]
Line of Credit Facility [Line Items]
Debt instrument, face amount	70,000,000
Credit Agreement [Member] | Delayed Draw Term Loan Facility [Member]
Line of Credit Facility [Line Items]
Debt instrument, face amount	$ 150,000,000
Long term debt outstanding			$ 0
Credit Agreement [Member] | Delayed Draw Term Loan Facility [Member] | First 12 Quarters Following the Closing [Member]
Line of Credit Facility [Line Items]
Periodic principal payment as percentage of aggregate principal amount	1.25%
Credit Agreement [Member] | Delayed Draw Term Loan Facility [Member] | Remaining Quarters Prior to Maturity [Member]
Line of Credit Facility [Line Items]
Periodic principal payment as percentage of aggregate principal amount	1.875%
Credit Agreement [Member] | Uncommitted Incremental Accordion Facility [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 100,000,000