Defined Contribution Benefit Plan (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012 Item	Dec. 31, 2011	Dec. 31, 2010
Defined Contribution Benefit Plan
Employer's matching contribution for every dollar the employees contribute (in cents)	$ 50	$ 50	$ 50
Employer's matching contribution, maximum	7,650	7,500	3,000
Employer's contribution as a percentage of employee's eligible compensation, maximum	3.00%	3.00%
Employer's matching contribution, vesting period		5 years
Number of foreign subsidiaries		1
Aggregate employer's contribution to pension plans		$ 2,500,000	$ 2,100,000	$ 1,700,000