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Income Per Share and Stockholders' Equity - Additional Information (Detail) - USD ($)	1 Months Ended		3 Months Ended		12 Months Ended
	Feb. 28, 2019	Jan. 31, 2019	Mar. 31, 2019	Mar. 31, 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
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					$ 250,000,000
Contingently Issuable Shares [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares excluded in computation of diluted income per share			547,676	69,346