Long-term Borrowings - Components of Long-term Borrowings (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Less: unamortized discount and debt issuance costs	$ (6,761)	$ (7,834)
Long-term borrowings, net of unamortized discount and debt issuance costs	304,489	303,416
Exchangeable Senior Notes [Member] \| 5.0% Exchangeable Senior Notes due March 2021 [Member]
Debt Instrument [Line Items]
Long-term borrowings	86,250	86,250
Senior Notes [Member] \| 6.625% Senior Notes Due 2021 [Member]
Debt Instrument [Line Items]
Long-term borrowings	$ 225,000	$ 225,000

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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