Employee Benefit Plans - Profit Sharing and Savings Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits
Eligibility requirement, service hours to be completed	20 hours
Deferred Profit Sharing
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits
Eligibility requirement, lesser of percent of compensation	100.00%
Eligibility requirement, lesser of annual contribution amount	$ 40,000
Eligibility requirement, requisite service period	P3Y
Compensation expense	2,063,000	1,480,000	1,197,000
Savings Plan, Employee Elected
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits
Compensation expense	4,034,000	3,905,000	3,896,000
Maximum annual contribution per employee, amount per dollar of employee contribution	$ 1.25
Maximum annual contribution per employee, percent	4.00%