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Income Per Share and Stockholders' Equity - Additional Information (Detail) - USD ($)	1 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended
	Feb. 28, 2019	Jan. 31, 2019	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Oct. 27, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares repurchased during the period, shares							3,980,656
Shares repurchased during the period, value					$ 45,088,000		$ 161,000,000.0
Payments for repurchase of additional shares					$ 45,088,000
Class A Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Authorized share repurchase term	3 years				3 years
Shares repurchased during the period, value					$ 11,000
Average price per share		$ 39.38					$ 40.43
Payments for repurchase of additional shares		$ 45,100,000
Shares repurchased during the period		1,144,449
Class A Common Stock [Member] | Maximum [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Authorized share repurchase amount	$ 300,000,000.0							$ 250,000,000.0
Contingently Issuable Shares [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares excluded in computation of diluted income per share			813,155	75,851	579,994	51,946

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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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