Benefit Plans - Savings and Reitirement Plans (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) saving_retirement_plan	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Benefit Plans
Number of plans sponsored by the company | saving_retirement_plan	2
Expenses related to the savings and retirement plan | $	$ 2.1	$ 1.8	$ 1.8
Savings and retirement plan
Benefit Plans
Employer match of first tier of employee contributions (as a percent)	50.00%
First tier percentage of compensation eligible for match by employer	6.00%