Financial Instruments	6 Months Ended
Financial Instruments	Jun. 30, 2016
Fair Value Disclosures [Abstract]
Financial Instruments	Financial Instruments The fair value of cash and cash equivalents, accounts payable, advances and amounts outstanding under the revolving credit facility approximates carrying value due to the short-term maturity of such instruments and floating interest rates. As of June 30, 2016, the fair value of trade accounts receivable approximated the carrying value due to the similarities in the initial and current discount rates. In addition, as of June 30, 2016, the fair value and the carrying value of the principal amount of the senior unsecured notes was $316.4 million and $300.0 million, respectively. The fair value of trade accounts receivable and the senior unsecured notes was determined (for purposes of these disclosures) using significant unobservable inputs by performing a discounted cash flow analysis and using current discount rates as appropriate for each type of instrument. The Company has short-term money market investments which are classified as cash and cash equivalents on the consolidated balance sheets. The fair value of these investments at June 30, 2016 and December 31, 2015 was measured based on quoted prices in active markets.

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.