Stock Plans and Stock Based Compensation (Stock Based Compensation Expense) (Details) (USD $)	12 Months Ended
Dec. 27, 2014	Dec. 28, 2013	Dec. 29, 2012	Dec. 31, 2011
Stock-based compensation
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 15.19	$ 11.17	$ 10.94
Expected life (in years)	4 years 2 months	4 years 2 months 12 days	4 years 6 months
Stock options, shares equivalent	1.0
Stock-based compensation	$ 31,035,000	$ 24,542,000	$ 21,855,000
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	675,927,000	644,077,000	603,200,000	527,363,000
Provision for income taxes	(11,006,000)	(8,658,000)	(7,793,000)
Net income attributable to common shareowners	20,029,000	15,884,000	14,062,000
Capitalized stock-based compensation related costs	0
Expected volatility (as a percent)	30.00%	33.00%	35.00%
Risk-free interest rate (as a percent)	1.55%	0.80%	0.84%
Expected dividend yield (as a percent)	0.00%	0.00%	0.00%
Pool of excess tax benefits	10,800,000crl_PoolOfExcessTaxBenefits	7,300,000crl_PoolOfExcessTaxBenefits	9,600,000crl_PoolOfExcessTaxBenefits
Adjustments to Additional Paid in Capital, Income Tax Deficiency from Share-based Compensation	4,300,000	1,100,000
Windfall Tax Benefit	1,600,000crl_WindfallTaxBenefit
Cost of sales
Stock-based compensation
Stock-based compensation	5,382,000	5,381,000	5,470,000
Selling and administration
Stock-based compensation
Stock-based compensation	25,653,000	19,161,000	16,385,000
Employee Stock Option [Member]
Stock-based compensation
Intrinsic value of options exercised	30,469,000	24,737,000	5,135,000
Performance Shares [Member]
Stock-based compensation
Stock-based compensation	$ 8,461,000	$ 2,171,000
Expected volatility (as a percent)	29.00%	32.00%
Risk-free interest rate (as a percent)	0.63%	0.38%
Expected dividend yield (as a percent)	0.00%	0.00%

Pool of excess tax benefits

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- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Options, Number of Shares Equivalent

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Windfall Tax Benefit

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Amount of decrease in additional paid in capital (APIC) resulting from a tax deficiency associated with a share-based compensation plan other than an employee stock ownership plan (ESOP).

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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The amount of expense, net of income tax, recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Represents the compensation cost capitalized during the period arising from equity-based compensation arrangements (for example, shares of stock, units, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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The risk-free interest rate assumption that is used in valuing an option on its own shares.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Amount of stockholders' equity (deficit), net of receivables from officers, directors, owners, and affiliates of the entity, attributable to both the parent and noncontrolling interests. Amount excludes temporary equity. Alternate caption for the concept is permanent equity.

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