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The percentage applied to the RSU valuation as determined by a monte carlo simulation.

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Employees may elect to receive bonuses or commissions in the form of common shares in lieu of cash ("Bonus Shares"). By making such election, the employee receives shares equal to this percentage of the cash value of the bonus or commission, less applicable withholding tax.

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Number of options for which the exercise price is higher than the Company's stock price.

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Number of options for which the exercise price is lower than the Company's share price.

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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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Aggregate number of common shares reserved for future issuance.

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The compensation expense recognized during the period pertaining to the deferred compensation arrangement.

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Aggregate proceeds received by the entity during the annual period from exercises of stock or unit options and conversion of similar instruments granted under equity-based payment arrangements.

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Unrecognized cost of unvested share-based compensation awards.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Unrecognized cost of unvested options awarded to employees as compensation.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Percentage of vesting of share-based compensation awards.

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Discount rate from fair value on purchase date that participants pay for shares.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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Period from grant date that an equity-based award expires, 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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The highest percentage of annual salary that an employee is permitted to utilize with respect to the plan.

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The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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 by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Weighted average remaining contractual term for fully vested and expected to vest options outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

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The ceiling of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

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Number of shares issued during the period as a result of an employee stock purchase plan.

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Share Based Compensation (Details) (USD $)	12 Months Ended
Share Based Compensation (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Options [Abstract]
Authorized number of shares under the Plan and the 2008 Plan	21,100,000
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]
Common shares reserved for future issuance under the Plan and the 2008 Plan	6,100,098	6,637,761	7,156,179
ESPP [Member]
Options [Abstract]
Allocated Share-based Compensation Expense	$ 104,000	$ 71,000	$ 99,000
Authorized number of shares under the Plan and the 2008 Plan	750,000
Long Term Incentive Shares [Abstract]
Allocated Share-based Compensation Expense	104,000	71,000	99,000
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]
Maximum percent of salary contributed	10.00%
Allocated Share-based Compensation Expense	104,000	71,000	99,000
Discount on market value of shares	15.00%
Shares issued	12,612	16,793	18,611
Stock Options [Member] \| Options [Member]
Options [Abstract]
option term	10 years
Option - Vesting Period	3 years
Allocated Share-based Compensation Expense	1,800,000	1,600,000	1,700,000
Weighted average fair value of options granted	$ 4.09	$ 7.18	$ 6.55
Exercise price for options outstanding lower limit	$ 20.32
Exercise price for options outstanding upper limit	$ 49.74
weighted average remaining contractual life of option outstanding	5 years 4 months 14 days
Weighted average remaining contractual life of options exercisable	4 years 0 months 1 day
Number of options outstanding and exercisable that had an exercise price higher than closing price of the Company's shares	565,000
Number of options outstanding and exercisable that had an exercise price lower than the Company's share price	1,200,000
Total intrinsic value of options exercised	310,000	4,900,000	5,900,000
Total cash received from the exercise of options	1,400,000	15,200,000	22,900,000
Unrecognized compensation costs related to nonvested options	324,000
Compensation costs not yet recognized, period for recognition	0 years 9 months 9 days
Aggregate intrinsic value of options	6,800,000
Long Term Incentive Shares [Abstract]
Long Term Incentive Shares - Vesting Period	3 years
Allocated Share-based Compensation Expense	1,800,000	1,600,000	1,700,000
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]
Allocated Share-based Compensation Expense	1,800,000	1,600,000	1,700,000
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Risk-free interest rate	1.60%	1.10%	1.10%
Volatility	23.60%	35.60%	37.70%
Stock Options [Member] \| First Portion [Member] \| Options [Member]
Options [Abstract]
Vesting percent	20.00%
Stock Options [Member] \| Second Portion [Member] \| Options [Member]
Options [Abstract]
Vesting percent	50.00%
Stock Options [Member] \| Third Portion [Member] \| Options [Member]
Options [Abstract]
Vesting percent	100.00%
Restricted Stock [Member] \| Long Term Incentive Shares [Member]
Options [Abstract]
Option - Vesting Period	5 years
Allocated Share-based Compensation Expense	9,000,000	9,100,000	8,700,000
Compensation costs not yet recognized, period for recognition	1 year 5 months 1 day
Long Term Incentive Shares [Abstract]
Weighted Average Grant Date Fair Value - Granted	$ 37.13	$ 39.42	$ 34.61
Long Term Incentive Shares - Vesting Period	5 years
Shares granted	263,000
Total unrecognized compensation cost related to nonvested shares	12,500,000
Total fair value of restricted shares vested	9,300,000	9,900,000	8,700,000
Allocated Share-based Compensation Expense	9,000,000	9,100,000	8,700,000
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]
Allocated Share-based Compensation Expense	9,000,000	9,100,000	8,700,000
Restricted Stock Units (RSUs) [Member] \| 2008 plan [Member] \| 2014 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Risk-free interest rate	0.68%
Volatility	24.00%
Restricted Stock Units (RSUs) [Member] \| 2008 plan [Member] \| 2013 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Risk-free interest rate		0.35%
Volatility		26.00%
Restricted Stock Units (RSUs) [Member] \| 2008 plan [Member] \| 2012 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Risk-free interest rate			0.52%
Volatility			41.00%
Restricted Stock Units (RSUs) [Member] \| First Portion [Member] \| 2008 plan [Member]
Options [Abstract]
Option - Vesting Period	3 years
Long Term Incentive Shares [Abstract]
Long Term Incentive Shares - Vesting Period	3 years
Restricted Stock Units (RSUs) [Member] \| Second Portion [Member] \| 2008 plan [Member]
Options [Abstract]
Option - Vesting Period	3 years
Long Term Incentive Shares [Abstract]
Long Term Incentive Shares - Vesting Period	3 years
Bonus Shares [Member] \| Bonus Shares [Member]
Options [Abstract]
Allocated Share-based Compensation Expense	3,900,000	3,100,000	2,900,000
Long Term Incentive Shares [Abstract]
Shares granted	103,834	79,271	80,573
Allocated Share-based Compensation Expense	3,900,000	3,100,000	2,900,000
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]
Percent Applied to Bonuses Taken in Cash	120.00%
Allocated Share-based Compensation Expense	3,900,000	3,100,000	2,900,000
Performance Shares [Member] \| Profit Sharing Plan [Member]
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]
Maximum percent of salary contributed	5.00%
Profit sharing plan expense	$ 543,000	$ 698,000	$ 564,000
Chief Executive Officer [Member] \| Restricted Stock Units (RSUs) [Member] \| Maximum [Member] \| 2013 [Member]
Options [Abstract]
Vesting percent		272.00%
Chief Executive Officer [Member] \| Restricted Stock Units (RSUs) [Member] \| Maximum [Member] \| 2012 [Member]
Options [Abstract]
Vesting percent			272.00%
Chief Executive Officer [Member] \| Restricted Stock Units (RSUs) [Member] \| 2008 plan [Member] \| 2014 [Member]
Options [Abstract]
Option - Vesting Period	3 years
Long Term Incentive Shares [Abstract]
Long Term Incentive Shares - Vesting Period	3 years
Chief Executive Officer [Member] \| Restricted Stock Units (RSUs) [Member] \| 2008 plan [Member] \| Maximum [Member] \| 2014 [Member]
Options [Abstract]
Vesting percent	272.00%
Chief Executive Officer [Member] \| Restricted Stock Units (RSUs) [Member] \| First Portion [Member] \| 2008 plan [Member] \| 2014 [Member]
Long Term Incentive Shares [Abstract]
Monte Carlo RSU Valuation	157.00%
Chief Executive Officer [Member] \| Restricted Stock Units (RSUs) [Member] \| First Portion [Member] \| 2008 plan [Member] \| 2013 [Member]
Long Term Incentive Shares [Abstract]
Monte Carlo RSU Valuation		150.00%
Chief Executive Officer [Member] \| Restricted Stock Units (RSUs) [Member] \| First Portion [Member] \| 2008 plan [Member] \| 2012 [Member]
Long Term Incentive Shares [Abstract]
Monte Carlo RSU Valuation			159.00%
Executives Other [Member] \| Restricted Stock Units (RSUs) [Member] \| Maximum [Member] \| 2013 [Member]
Options [Abstract]
Vesting percent		200.00%
Executives Other [Member] \| Restricted Stock Units (RSUs) [Member] \| Maximum [Member] \| 2012 [Member]
Options [Abstract]
Vesting percent			200.00%
Executives Other [Member] \| Restricted Stock Units (RSUs) [Member] \| 2008 plan [Member] \| 2014 [Member]
Options [Abstract]
Option - Vesting Period	3 years
Long Term Incentive Shares [Abstract]
Long Term Incentive Shares - Vesting Period	3 years
Executives Other [Member] \| Restricted Stock Units (RSUs) [Member] \| 2008 plan [Member] \| Maximum [Member] \| 2014 [Member]
Options [Abstract]
Vesting percent	200.00%
Executives Other [Member] \| Restricted Stock Units (RSUs) [Member] \| First Portion [Member] \| 2008 plan [Member] \| 2014 [Member]
Long Term Incentive Shares [Abstract]
Monte Carlo RSU Valuation	125.00%
Executives Other [Member] \| Restricted Stock Units (RSUs) [Member] \| First Portion [Member] \| 2008 plan [Member] \| 2013 [Member]
Long Term Incentive Shares [Abstract]
Monte Carlo RSU Valuation		121.00%
Executives Other [Member] \| Restricted Stock Units (RSUs) [Member] \| First Portion [Member] \| 2008 plan [Member] \| 2012 [Member]
Long Term Incentive Shares [Abstract]
Monte Carlo RSU Valuation			127.00%