Employee Benefit Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Employee Benefit Plans
Employee benefit plan expense	$ 20,651,000	$ 18,770,000	$ 16,548,000
CPE Inc. plans
Employee Benefit Plans
Employee benefit plan expense	19,762,000	18,098,000	15,922,000
Decker Pension Plan
Employee Benefit Plans
Employee benefit plan expense	889,000	672,000	626,000
Changes in the accumulated postretirement benefit obligation
Long-term APBO	5,300,000	5,400,000
Decker Pension Plan
Share of funded status of the plan reported in noncurrent other liabilities	5,300,000	5,400,000
Defined contribution retirement plans | CPE Inc. plans
Employee Benefit Plans
Employee benefit plan expense	12,550,000	12,496,000	11,212,000
Defined Contribution Retirement Plans
Number of sponsored defined contribution and profit sharing plans	2
Employer's matching contribution limit per calendar year (as a percent)	6.00%
Employer's contribution under profit sharing plan (as a percent)	6.00%
Contributions	12,550,000	12,496,000	11,212,000
Retiree Medical Plan
Components of net periodic postretirement benefit costs
Service Cost	4,213,000	3,016,000	2,316,000
Interest Cost	1,424,000	1,281,000	989,000
Amortization of prior service cost	1,575,000	1,305,000	1,406,000
Net periodic postretirement benefit cost	7,212,000	5,602,000	4,711,000
Changes in the accumulated postretirement benefit obligation
Balance at the beginning of the period	33,166,000	23,271,000	16,379,000
Current period service costs	4,213,000	3,016,000	2,316,000
Interest Cost	1,424,000	1,281,000	989,000
Change in actuarial assumptions	4,590,000	5,598,000	3,587,000
Balance at the end of the period	43,393,000	33,166,000	23,271,000
Less current portion	231,000	37,000	37,000
Long-term APBO	43,162,000	33,129,000	23,234,000
Assumptions in the measurement of the APBO
Discount rate (as a percent)	3.87%	4.30%	5.51%
Health care cost trend rate assumed for next year (as a percent)	7.50%	8.00%	8.50%
Ultimate health care cost trend rate (as a percent)	5.00%	5.00%	5.00%
Year that the rate reaches the ultimate trend rate	2018	2018	2018
Effect of one-percentage-point increase/decrease in assumed health care cost trend
Effect of one-percentage-point increase on net periodic postretirement benefit cost	878,000
Effect of one-percentage-point increase on APBO	8,100,000
Effect of one-percentage-point decrease on net periodic postretirement benefit cost	718,000
Effect of one-percentage-point decrease on APBO	6,500,000
Estimated future benefit payments:
2013	231,000
2014	385,000
2015	578,000
2016	826,000
2017	1,149,000
2018 - 2022	11,519,000
Decker Pension Plan
Share of funded status of the plan reported in noncurrent other liabilities	43,162,000	33,129,000	23,234,000
Retiree Medical Plan | CPE Inc. plans
Employee Benefit Plans
Employee benefit plan expense	$ 7,212,000	$ 5,602,000	$ 4,710,000
Retiree Medical Plan
Age of employees, entitled to receive benefits under the Retiree Medical Plan (in years)	55 years
Minimum completed term of service, employees entitled to receive benefits under the Retiree Medical Plan (in years)	10 years