Annual report pursuant to Section 13 and 15(d)

Transactions with Affiliates (Details)

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Transactions with Affiliates (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Allocation of costs      
Direct labor expenses $ 6.4 $ 4.0 $ 3.0
General and administrative expense $ 54.1 $ 49.6 $ 44.2