Employee 401(k) Plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Employee 401(k) Plan
Maximum percentage of pretax salary, which can be deferred by employees	20.00%
Maximum amount of wages, which can be deferred by employees	$ 18,000
Maximum amount of wages, which can be deferred by employees at least 50 years of age	$ 24,000
Minimum age of employees for a specified contribution amount of wages	50 years
Percentage of employee's salary for which the company contributes a matching contribution	50.00%
Maximum percentage of employee's salary for which the company contributes a matching contribution	8.00%
Amount of employer contribution	$ 400,000	$ 300,000	$ 300,000