Equity - Schedule of Changes in Number of Shares of Common Stock Issued and Repurchased (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Common Stock | Class A
Balance at beginning of period (in shares)	15,281
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (in shares)	4	12,811
Share conversion - Class B to A (in shares)	2,815	2,467
Shares issued under 2018 ESPP (in shares)		3
Balance at end of period (in shares)	18,100	15,281
Common Stock | Class B
Balance at beginning of period (in shares)	55,284
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Redesignation of common stock, (in shares)		57,185
Share conversion - Class B to A (in shares)	(2,815)	(2,467)
Vesting of restricted share grants (in shares)	522	215
Exercise of options (in shares)	946	351
Balance at end of period (in shares)	53,937	55,284
Common Stock | Pre-IPO
Balance at beginning of period (in shares)		57,182	56,505
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (in shares)			296
Redesignation of common stock, (in shares)		(57,184)
Vesting of restricted share grants (in shares)		2	389
Equity awards modified to liabilities (in shares)			(8)
Balance at end of period (in shares)			57,182
Treasury Stock | Class A
Balance at beginning of period (in shares)	(856)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Repurchase of shares	(829)	(856)
Balance at end of period (in shares)	(1,685)	(856)
Treasury Stock | Class B
Balance at beginning of period (in shares)	(2,147)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Redesignation of common stock, (in shares)		(2,064)
Repurchase of shares		(83)
Shares withheld related to net settlement of equity awards (in shares)	(509)
Balance at end of period (in shares)	(2,656)	(2,147)
Treasury Stock | Pre-IPO
Balance at beginning of period (in shares)		(2,064)	(1,720)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Redesignation of common stock, (in shares)		2,064
Vesting of restricted share grants (in shares)			(344)
Balance at end of period (in shares)			(2,064)