The per share amount of a dividend declared, but not paid, as of the financial reporting date.

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Carrying value as of the balance sheet date of dividends declared but unpaid on equity securities issued by the entity and outstanding.

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Date the dividend to be paid was declared, in CCYY-MM-DD format.

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Date the holder must own the stock to be entitled to the dividend, in CCYY-MM-DD format.

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Equity impact of cash dividends declared by an entity during the period and applicable to holders of share-based compensation, such as non-vested shares, stock options, or restricted stock units. This element includes paid and unpaid dividends declared during the period.

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As of the balance sheet date, the aggregate unrecognized cost of equity-based awards made to employees under equity-based compensation awards that have yet to vest.

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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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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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The discount rate from market value on purchase date that participants pay for shares.

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

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Description of pertinent provisions of equity-based compensation awards that have actual or potential impact upon the company's financial statements.

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Stockholders' Equity (Narrative) (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	1 Months Ended	3 Months Ended	6 Months Ended			3 Months Ended						6 Months Ended
	May 11, 2012	Jun. 30, 2012	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 DRIP Accounts [Member]	Jun. 30, 2012 Stock Option [Member]	Mar. 31, 2012 Stock Option [Member]	Jun. 30, 2012 Stock Option [Member] Minimum [Member]	Jun. 30, 2012 Stock Option [Member] Maximum [Member]	Jun. 30, 2012 Restricted Stock Units [Member]	Mar. 31, 2012 Restricted Stock Units [Member]	Jun. 30, 2012 Restricted Stock Units [Member]	Jun. 30, 2011 Restricted Stock Units [Member]	Jun. 30, 2012 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for grant		10,215	10,215		4,843									1,535
Declared dividends per share	$ 0.25
Accrued dividends		$ 44,079	$ 44,079	$ 40,351
Quarterly cash dividend payable date	Sep. 03, 2012
Dividend record date		Jul. 06, 2012
Vesting period, maximum years							3 years	1 year	3 years		3 years
Maximum terms		seven
Unrecognized compensation cost						5,243				5,948		5,948
Weighted-average period in years, unrecognized compensation cost						1 year 9 months 18 days				1 year 1 month 6 days
Accrued dividend equivalents												$ 399	$ 392
Lesser of fair market value			90.00%
Shares issued			57