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Employee Benefit Plans - 401(k) Plan (Details) - Employee 401(k) Plan - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Defined Contribution Plan      
Employer matching contribution, percentage of match 6.00%    
Employer's matching contribution on the dollar for the first 6 percent of participant contributions 35.00%    
Contribution expense $ 10.7 $ 6.8 $ 2.1