Revolving Credit Facility - Narrative (Details)			12 Months Ended
	Feb. 22, 2016	Aug. 02, 2010 USD ($)	Dec. 31, 2017 USD ($)
Line of Credit Facility [Line Items]
Line of Credit Facility, Expiration Date			Sep. 25, 2019
Ratio of Indebtedness to Net Capital			3.0
Debt Instrument, Convertible, Conversion Ratio			5.0
Revolving Credit Facility | August 2010 Credit Facility Agreement
Line of Credit Facility [Line Items]
Maximum borrowing capacity on line of credit		$ 175,000,000
Increase to borrowing capacity		$ 50,000,000
Unused capacity			$ 32,400,000
Borrowings to be drawn			$ 800,000
Maximum leverage ratio		3.0
Minimum interest coverage ratio		5
Base Rate
Line of Credit Facility [Line Items]
Additional basis on borrowings	110.00%
Minimum
Line of Credit Facility [Line Items]
Additional basis on borrowings			125.00%
Minimum | Eurodollar
Line of Credit Facility [Line Items]
Additional basis on borrowings			25.00%
Minimum | Eurodollar | Revolving Credit Facility | August 2010 Credit Facility Agreement
Line of Credit Facility [Line Items]
Additional basis on borrowings		1.25%
Minimum | Base Rate | Revolving Credit Facility | August 2010 Credit Facility Agreement
Line of Credit Facility [Line Items]
Additional basis on borrowings		0.25%
Maximum
Line of Credit Facility [Line Items]
Additional basis on borrowings			250.00%
Maximum | Eurodollar
Line of Credit Facility [Line Items]
Additional basis on borrowings			150.00%
Maximum | Eurodollar | Revolving Credit Facility | August 2010 Credit Facility Agreement
Line of Credit Facility [Line Items]
Additional basis on borrowings		2.50%
Maximum | Base Rate | Revolving Credit Facility | August 2010 Credit Facility Agreement
Line of Credit Facility [Line Items]
Additional basis on borrowings		1.50%
International [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity on line of credit			$ 5,000,000.0
Unused capacity			$ 4,700,000