Fair Values of Financial Instruments - Additional Information (Detail)	9 Months Ended	12 Months Ended
Sep. 30, 2016	Dec. 31, 2015
4.97% Series A Senior Notes, Due October 5th 2020
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Current market rates used in measuring fair value	6.09%	6.66%
4.27% Series B Senior Notes, Due June 14th 2022
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Current market rates used in measuring fair value	6.33%	6.95%

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.

No definition available.

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