401(k) Savings Plan (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Compensation and Retirement Disclosure [Abstract]
Matching contribution vesting period	6 years
Plan expense	$ 1.3	$ 1.3	$ 1.0