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Commitments and Contingencies - Narratives (Details)
$ in Millions
 12 Months Ended 24 Months Ended 48 Months Ended
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Dec. 31, 2013
USD ($)
Dec. 31, 2015
USD ($)
case
Dec. 31, 2015
USD ($)
Loss contingency          
Rent expense $ 10.9 $ 9.8 $ 9.9    
Accrued liability for the outcomes of non-income based tax audits 2.7     $ 2.7 $ 2.7
Indemnified liabilities 1.5     $ 1.5 1.5
Litigation and Claims          
Number of heavy equipment statutes cases tried and completed in Texas state district court (cases) | case       3  
Number of heavy equipment statues cases appealed (cases) | case       3  
Ad valorem tax benefit 16.0       44.0
Ad valorem tax benefit agreed to by a number of appraisal review boards and county appraisal districts 10.2     $ 10.2 10.2
Ad valorem tax benefit in litigation $ 33.8     $ 33.8 $ 33.8