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Share Based Compensation Arrangement By Share Based Payment Award Maximum Share Value Authorized For Purchase Under Employee Stock Purchase Plan

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Unrecognized cost of unvested share-based awards, other than 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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-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

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Percentage of vesting of share-based compensation awards.

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

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

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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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Weighted average remaining contractual term for equity-based awards excluding options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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-Name Accounting Standards Codification

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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 highest percentage of annual salary that an employee is permitted to utilize with respect to the plan.

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The highest quantity of shares an employee can purchase under the plan per period.

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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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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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Number of share instruments newly issued under a share-based compensation plan.

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

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

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Stock Option Plans, Stock Grants, Stock Appreciation Rights and Employee Stock Purchase Plan - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2005	Apr. 30, 2013	Apr. 30, 2009
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance based shares that vested	183,716	133,482	138,321
Fair value of total vested shares	$ 5,100,000	$ 3,500,000	$ 4,600,000
Percentage of employees base compensation through payroll that can be invested for the purchase of common stock, maximum	10.00%
Number of shares which can be acquired by employee, maximum	1,000
Total market value of shares that can be acquired by employee	25,000
Employee Stock Purchase Plan, shares to be purchased in following period	9,509
Employee Stock Purchase Plan, shares purchased by employees	19,386	17,000	16,000
Discount on employee stock purchase plan	10.00%
Performance Based Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance based shares that vested	0	15,714	0
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options expiration term (in years)	10 years
Options and Non Performance Based Grants \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based payment award, award vesting period	3 years
Options and Non Performance Based Grants \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based payment award, award vesting period	4 years
Non Performance Based Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based payment award, award vesting period	5 years
Performance based shares that vested	90,263	60,183	91,323
Non Performance Based Shares \| Year Three
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting over the period	33.33%
Non Performance Based Shares \| Year Four
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting over the period	33.33%
Non Performance Based Shares \| Year Five
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting over the period	33.33%
Performance Based Shares Issued in 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of remaining shares vesting over the period dependent on compound annual growth book value per share immediately prior to vesting date	100.00%
Performance Based Shares Issued in 2014 \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting over the period	50.00%
Performance Based Shares Issued in 2014 \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting over the period	150.00%
Performance Based Shares Issued Between 2011-2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting over the period	50.00%
Percentage of remaining shares vesting over the period dependent on compound annual growth book value per share immediately prior to vesting date	50.00%
Performance Based Shares Issued Between 2011-2013 \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting over the period	0.00%
Performance Based Shares Issued Between 2011-2013 \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting over the period	150.00%
Performance Based Shares Issued Prior to 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based payment award, award vesting period	5 years
Performance Based Shares Issued Prior to 2011 \| Year Three
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting over the period	33.33%
Performance Based Shares Issued Prior to 2011 \| Year Four
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting over the period	33.33%
Performance Based Shares Issued Prior to 2011 \| Year Five
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting over the period	33.33%
Performance Based Shares Issued Prior to 2011 \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting over the period	0.00%
Performance Based Shares Issued Prior to 2011 \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vesting over the period	150.00%
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value of all RSU granted	$ 60.75	$ 55.36	$ 48.21
Unrecognized compensation expense, net of estimated forfeitures	16,300,000	10,600,000
Weighted Average Periods	2 years 3 months 18 days	2 years 3 months 12 days
Aggregate fair value of all unvested RSU	$ 46,100,000	$ 39,600,000
Employee stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise price as percentage of fair market value	90.00%
2005 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock authorized for issuance				1,000,000
Amended And Restated 2005 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock authorized for issuance					2,000,000	1,500,000
Stock issued during period under incentive plan	1,523,228
Number of stock available to be issued	476,772