Employee Benefit Plans - Employee Savings Plans (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) item	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
401(K) Plan
Number of 401(k) employee savings plans | item	2
Company contributions | $	$ 5.1	$ 5.0	$ 5.1
Union employees | Maximum
401(K) Plan
Company matching employee contributions (as a percent)	10.00%
Non-union employees
401(K) Plan
Company matching employee contributions (as a percent)	6.00%