Schedule I - Condensed Balance Sheets (Parenthetical) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Condensed Balance Sheet Statements, Captions [Line Items]
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	100,000,000us-gaap_PreferredStockSharesAuthorized	100,000,000us-gaap_PreferredStockSharesAuthorized
Preferred stock, shares issued	0us-gaap_PreferredStockSharesIssued	0us-gaap_PreferredStockSharesIssued
Preferred stock, shares outstanding	0us-gaap_PreferredStockSharesOutstanding	0us-gaap_PreferredStockSharesOutstanding
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	1,000,000,000us-gaap_CommonStockSharesAuthorized	1,000,000,000us-gaap_CommonStockSharesAuthorized
Common stock, shares issued	90,191,100us-gaap_CommonStockSharesIssued	89,900,453us-gaap_CommonStockSharesIssued
Treasury stock, shares	4,105,970us-gaap_TreasuryStockShares	1,500,000us-gaap_TreasuryStockShares
Parent Company [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	100,000,000	100,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	1,000,000,000	1,000,000,000
Common stock, shares issued	90,191,100	89,900,453
Treasury stock, shares	4,105,970	1,500,000

Face amount or stated value per share of common stock.

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The maximum number of common shares permitted to be issued by an entity's charter and bylaws.

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Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

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Face amount or stated value per share of preferred stock nonredeemable or redeemable solely at the option of the issuer.

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The maximum number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws.

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Total number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) issued to shareholders (includes related preferred shares that were issued, repurchased, and remain in the treasury). May be all or portion of the number of preferred shares authorized. Excludes preferred shares that are classified as debt.

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Aggregate share number for all nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) held by stockholders. Does not include preferred shares that have been repurchased.

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Number of common and preferred shares that were previously issued and that were repurchased by the issuing entity and held in treasury on the financial statement date. This stock has no voting rights and receives no dividends.

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