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Retirement Savings Plan	12 Months Ended
Retirement Savings Plan	Dec. 31, 2017
Retirement Benefits [Abstract]
Retirement Savings Plan	Retirement Savings Plan The Company sponsors a defined contribution 401(k) retirement plan (the “401(k) Plan”) covering all employees who meet certain age and service requirements. Employees may contribute a percentage of their eligible compensation into the 401(k) Plan, subject to certain limitations imposed by the Internal Revenue Code. Through December 31, 2017, the Company matched employees’ contributions at a rate of 100% of employees’ contributions up to the first 3.0% and 50.0% of the next 2.0% of the employees’ compensation contributed to the 401(k) Plan. The Company’s matching contributions were $2.8 million, $2.4 million and $2.1 million in 2017, 2016 and 2015, respectively.