Exchangeable Senior Notes - Additional Information (Detail) - Exchangeable Senior Notes due May 1, 2020 [Member]	12 Months Ended
Dec. 31, 2016 USD ($) $ / shares
Debt Instrument [Line Items]
Issuance of debt through private offering	$ 250,000,000
Percentage of interest on debt	5.375%
Number of shares exchanged per exchangeable notes	33.8667
Principal amount of the exchangeable notes	$ 1,000
Increased in cash dividend \| $ / shares	$ 0.57
Maturity date of debt instrument	May 01, 2020
Initial Exchangeable Rate [Member]
Debt Instrument [Line Items]
Number of shares exchanged per exchangeable notes	33.5149

Exchangeable Senior Notes Per Note Principal Amount

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Increase In Quarterly Cash Dividend In Common Stock

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Ratio applied to the conversion of debt instrument into equity with equity shares divided by debt principal amount.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

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Carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer), excluding current portion. Senior note holders are paid off in full before any payments are made to junior note holders.

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