Fair Value Measurement - Estimated Fair Values (Details) - USD ($) $ in Thousands		Sep. 30, 2017	Dec. 31, 2016
Financial Assets:
Restricted investments, Carrying Value	[1]	$ 22,303	$ 0
Restricted investments, Estimated Fair Value	[1]	22,297	0
Money market funds, carrying value	[2]	1,597	1,385
Money market funds, fair value	[2]	1,597	1,385
Debt securities - municipal securities	[2]	1,728	1,903
Financial Liabilities:
Term loan, due October 2020, Carrying Value		399,749	0
Accounts receivable securitization, due January 2019, Carrying Value		285,000	0
Accounts receivable securitization, due January 2019, Estimated Fair Value		285,000	0
Revolving line of credit, Carrying Value		85,000	18,000
Deferred loan costs		2,312	0
Loans Payable [Member] | 2017 Agreement, Credit Facility [Member]
Financial Liabilities:
Term loan, due October 2020, Carrying Value	[3],[4]	399,296	0
Term loan, due October 2020, Estimated Fair Value	[3]	400,000	0
Deferred loan costs		704	0
Line of Credit [Member] | 2017 Agreement, Credit Facility [Member]
Financial Liabilities:
Revolving line of credit, Carrying Value	[4],[5]	85,000	0
Revolving line of credit, Estimated Fair Value		85,000	0
Line of Credit [Member] | 2013 Knight Agreement [Member]
Financial Liabilities:
Revolving line of credit, Carrying Value	[4],[6]	0	18,000
Revolving line of credit, Estimated Fair Value		$ 0	$ 18,000

[1] Restricted investments are included in "Restricted investments, held to maturity, amortized cost."

[2] Items included within "Other long-term assets, restricted cash and investments."

[3] Carrying value is net of $0.7 million deferred loan costs as of September 30, 2017.

[4] Refer to Note 21 for information regarding the fair value of long-term debt.

[5] The Company also had outstanding letters of credit under the Revolver of $124.8 million at September 30, 2017

[6] also had outstanding letters of credit under the Knight Revolver of $31.3 million at December 31, 2016