Net Income Per Share - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dividends declared per share, in dollars per share	$ 0.75	$ 0.73	$ 2.21	$ 2.11
Net income allocated to PRS	$ 0.2	$ 0.1	$ 0.5	$ 0.6
Employee Stock Option
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stock excluded from computation of diluted net income per share	0	0	0	0
Stock-Settled Appreciation Rights (SARs)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stock excluded from computation of diluted net income per share	2,668	2,647	2,322.5	1,323.5

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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-Topic 260
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Aggregate dividends declared during the period for each share of common stock outstanding.

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-Publisher FASB
-Name Accounting Standards Codification
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Amount of earnings (loss) distributed and earnings (loss) allocated to participating securities for the basic earnings (loss) per share or per unit calculation under the two-class method.

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