401(k) Plan (Details Textual) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Retirement Plan (Textual) [Abstract]
Period to become eligible to participate in 401(k) Plan	6 months
Matching contributions to voluntary retirement plan	$ 1.7	$ 1.6	$ 1.5