Employee Benefits - Narrative (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
401 (k) Retirement Plan [Abstract]
Minimum service period for plan eligibility	6 months
Minimum allowable contribution to the plan by each employee, percent	1.00%
Maximum allowable contribution to the plan by each employee, percent	80.00%
Employers matching contribution, vesting period	4 years
Company contributions to the plan	$ 1.1	$ 1.1	$ 1.1
Range 1
401 (k) Retirement Plan [Abstract]
Employer matching contribution, percent	100.00%
Employer matching contribution, percent of employee's gross pay	2.00%
Range 2
401 (k) Retirement Plan [Abstract]
Employer matching contribution, percent	50.00%
Employer matching contribution, percent of employee's gross pay	2.00%