Employee Benefit Plans (Details 3) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Employee Retirement Plan
Employer's matching contribution, percentage	40.00%
Period of service for vesting of matching contributions	3 years
Annual increments for vesting in employer's matching contribution	0.33
Period over which the matching contribution vest annually	3 years
Expenses related to 401 (k) plan	$ 2.1	$ 1.7	$ 1.4