Employee Stock Purchase Plan and 401(k) Plan - 401(k) Profit Sharring Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Defined contribution plan, maximum annual contributions per employee (as a percent)	40.00%
Defined contribution plan, employer matching contribution, percent of match	37.50%
Defined contribution plan, employe matching contribution, percent of employee's gross pay	6.00%
Defined contribution plan, cost recognized	$ 6.3	$ 5.8	$ 5.5