401(k) Savings Plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]
401(k) employer matching percentage	50.00%
Maximum 401(k) annual contributions by employer per employee	$ 2,400
401(k) vesting period	4 years
401(k) matching contribution expenses	$ 1,900,000	$ 1,600,000	$ 1,300,000