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Retirement Plans - Defined Contribution Plans (Details) - 401k Plan - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Defined Contribution Plan Disclosure [Line Items]      
Eligible employee contribution maximum (percentage) 85.00%    
Defined contribution plan, employment eligibility to receive matching contributions, minimum (in years) 6 months    
Defined contribution plan, percentage of eligible employee contribution match, first tier 100.00%    
Defined contribution plan, percentage of eligible employee contributions matched fully, first tier 3.00%    
Defined contribution plan, eligible employee contribution match, second tier 50.00%    
Defined contribution plan, eligible employee contribution matched by the company, second tier 2.00%    
Defined contribution plan, cost recognized $ 6.7 $ 7.3 $ 5.0