Credit Facility	12 Months Ended
Dec. 31, 2017
Debt Disclosure [Abstract]
Credit Facility	Credit Facility February 2015 Amended Credit Facility In February 2015, the Company entered into a third amended and restated loan and security agreement (“Third Amended Credit Facility”) with the same financial institution with which the Company had previous credit arrangements, effective as of February 18, 2015, for a $35.0 million secured revolving credit facility that expires on February 18, 2018. The Third Amended Credit Facility provides a $10.0 million subfacility for the issuance of letters of credit and contains an increase option permitting the Company, subject to the lenders consent, to increase the revolving credit facility by up to $15.0 million, to an aggregate maximum of $50 million. This amended credit facility bears interest, at the Company’s option, at either (i) the prime rate published by The Wall Street Journal, plus a spread of -0.25% to 0.50%, or (ii) a LIBOR rate determined in accordance with the terms of the credit facility, plus a spread of 1.75% to 2.50%. In each case, the spread is based on the Company’s adjusted quick ratio, which is a ratio of the Company’s cash and cash equivalents plus net billed accounts receivable to current liabilities plus all borrowings under the credit facility. Interest is due and payable quarterly in arrears for prime rate loans and on the earlier of the last day of each quarter or the end of an interest period, as defined in the Third Amended Credit Facility, for LIBOR rate loans. The Company is also obligated to pay an unused revolving line facility fee of 0.0% to 0.20% per annum based on the Company’s adjusted quick ratio. This amended credit facility requires the Company to maintain an adjusted quick ratio of at least 1.5 to 1 on the last day of each quarter. If the adjusted quick ratio is not maintained, then the facility requires the Company to maintain, as measured at each quarter end, a maximum consolidated leverage ratio 3.00 or 2.50 to 1.00, and a fixed charge coverage ratio of at least 1.25 to 1.00. Consolidated leverage ratio is a ratio of all funded indebtedness, including all capital lease obligations, plus all letters of credit under the facility to the Company’s Adjusted EBITDA for the trailing twelve months. Fixed charge coverage ratio is the ratio of the Company's Adjusted EBITDA minus cash income taxes to its cash interest payments plus capital expenditures for the trailing twelve months. This credit facility also limits the Company’s ability to pay dividends. At December 31, 2017 and 2016, the Company was in compliance with the financial covenants. The Company’s future material domestic subsidiaries are required, upon the lender’s request, to become co-borrowers under the credit facility. The credit facility contains acceleration clauses that accelerate any borrowings in the event of default. The obligations of the Company and its future material domestic subsidiaries are collateralized by substantially all of their respective assets, subject to certain exceptions and limitations. At December 31, 2017 and 2016, the Company had no outstanding amounts under the credit facility. At December 31, 2017 and 2016, the amounts available were $31.0 million and $30.7 million, respectively, reduced for letters of credit issued and outstanding under the subfacility of $4.0 million and $4.3 million, respectively. February 2018 Amendment to Credit Facility In February 2018, the Company entered into a first amendment to the Third Amended Credit Facility (“First Amendment”). The First Amendment extends the maturity date to February 18, 2021 and amends, among other things, the maximum consolidated leverage ratio covenant and the fixed charge coverage ratio definition, which is now defined as the ratio of the Company’s Adjusted EBITDA minus cash income taxes and capital expenditures to its cash interest payments measured on a trailing twelve-month basis.

Credit Facility

February 2015 Amended Credit Facility

In February 2015, the Company entered into a third amended and restated loan and security agreement (“Third Amended Credit Facility”) with the same financial institution with which the Company had previous credit arrangements, effective as of February 18, 2015, for a $35.0 million secured revolving credit facility that expires on February 18, 2018. The Third Amended Credit Facility provides a $10.0 million subfacility for the issuance of letters of credit and contains an increase option permitting the Company, subject to the lenders consent, to increase the revolving credit facility by up to $15.0 million, to an aggregate maximum of $50 million.

This amended credit facility bears interest, at the Company’s option, at either (i) the prime rate published by The Wall Street Journal, plus a spread of -0.25% to 0.50%, or (ii) a LIBOR rate determined in accordance with the terms of the credit facility, plus a spread of 1.75% to 2.50%. In each case, the spread is based on the Company’s adjusted quick ratio, which is a ratio of the Company’s cash and cash equivalents plus net billed accounts receivable to current liabilities plus all borrowings under the credit facility.

Interest is due and payable quarterly in arrears for prime rate loans and on the earlier of the last day of each quarter or the end of an interest period, as defined in the Third Amended Credit Facility, for LIBOR rate loans. The Company is also obligated to pay an unused revolving line facility fee of 0.0% to 0.20% per annum based on the Company’s adjusted quick ratio.

This amended credit facility requires the Company to maintain an adjusted quick ratio of at least 1.5 to 1 on the last day of each quarter. If the adjusted quick ratio is not maintained, then the facility requires the Company to maintain, as measured at each quarter end, a maximum consolidated leverage ratio 3.00 or 2.50 to 1.00, and a fixed charge coverage ratio of at least 1.25 to 1.00.

Consolidated leverage ratio is a ratio of all funded indebtedness, including all capital lease obligations, plus all letters of credit under the facility to the Company’s Adjusted EBITDA for the trailing twelve months. Fixed charge coverage ratio is the ratio of the Company's Adjusted EBITDA minus cash income taxes to its cash interest payments plus capital expenditures for the trailing twelve months. This credit facility also limits the Company’s ability to pay dividends. At December 31, 2017 and 2016, the Company was in compliance with the financial covenants.

The Company’s future material domestic subsidiaries are required, upon the lender’s request, to become co-borrowers under the credit facility. The credit facility contains acceleration clauses that accelerate any borrowings in the event of default. The obligations of the Company and its future material domestic subsidiaries are collateralized by substantially all of their respective assets, subject to certain exceptions and limitations.

At December 31, 2017 and 2016, the Company had no outstanding amounts under the credit facility. At December 31, 2017 and 2016, the amounts available were $31.0 million and $30.7 million, respectively, reduced for letters of credit issued and outstanding under the subfacility of $4.0 million and $4.3 million, respectively.

February 2018 Amendment to Credit Facility

In February 2018, the Company entered into a first amendment to the Third Amended Credit Facility (“First Amendment”). The First Amendment extends the maturity date to February 18, 2021 and amends, among other things, the maximum consolidated leverage ratio covenant and the fixed charge coverage ratio definition, which is now defined as the ratio of the Company’s Adjusted EBITDA minus cash income taxes and capital expenditures to its cash interest payments measured on a trailing twelve-month basis.