Retirement Plans and Employee Stock Purchase Plans (Details 2) (2009 Stock Purchase Plan, USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
2009 Stock Purchase Plan
Employee Stock Purchase Plans
Service period required to be completed for an employee to be eligible to participate in plan, minimum (in days)	90
Ownership interest in Company common stock to disqualify employee from participation in plan, maximum (as a percent)	5.00%
Discount rate at which common stock can be purchased by the plan participant (as a percent)	5.00%
Maximum percentage of base salary which can be contributed by the employees	15.00%
Maximum amount of base salary which can be contributed annually by the employees	$ 21,250
Summary of purchases made under the 2010 and 1995 Employee Stock Purchase Plans
Number of shares purchased	487,451	300,177	356,777
Average price of shares purchased (in dollars per share)	$ 8.35	$ 14.56	$ 13.52