Stockholders' Equity (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Mar. 16, 2020	May 01, 2018
Shelf Registration [Member]
Class of Stock [Line Items]
Common stock shares issued for cash (in shares)	0	0
Common Class A [Member] | Stock Repurchase Program [Member]
Class of Stock [Line Items]
Stock repurchase program, authorized amount			$ 250,000,000
Stock repurchase program expiry date	Sep. 30, 2021
Stock repurchased during period	$ 0
Common Class A [Member] | Equity Distribution Agreement [Member]
Class of Stock [Line Items]
Common stock, shares sold (in shares)	842,412
Common stock, shares available to be sold	$ 336,668,000
Common Class A [Member] | Maximum [Member]
Class of Stock [Line Items]
Aggregate offering price of common stock issuable				$ 400,000,000