CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Common Stock and Additional Paid-In Capital	Retained Earnings (Accumulated Deficit)	Accumulated Other Comprehensive Income
Beginning balance at Dec. 31, 2020	$ 607,000	$ 747,000	$ (144,000)	$ 4,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock from exercise of stock options		1,000
Issuance of common stock for employee stock purchase plan		5,000
Stock based compensation expense		37,000
Net income	269,000		269,000
Repurchase of common stock			(94,000)
Awards effectively repurchased for required employee withholding taxes			(13,000)
Other comprehensive income/(loss)	(3,000)			(3,000)
Ending balance at Sep. 30, 2021	809,000	790,000	18,000	1,000
Beginning balance at Jun. 30, 2021	744,000	776,000	(35,000)	3,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock from exercise of stock options		1,000
Stock based compensation expense		13,000
Net income	77,000		77,000
Repurchase of common stock			(20,000)
Awards effectively repurchased for required employee withholding taxes			(4,000)
Other comprehensive income/(loss)	(2,000)			(2,000)
Ending balance at Sep. 30, 2021	809,000	790,000	18,000	1,000
Beginning balance at Dec. 31, 2021	881,000	808,000	74,000	(1,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock from exercise of stock options		1,000
Issuance of common stock for employee stock purchase plan		5,000
Issuance of common stock for the acquisition of Zenefits		17,000
Stock based compensation expense		47,000
Net income	307,000		307,000
Repurchase of common stock	(380,000)		(383,000)
Awards effectively repurchased for required employee withholding taxes			(15,000)
Other comprehensive income/(loss)	(4,000)
Ending balance at Sep. 30, 2022	856,000	878,000	(17,000)	(5,000)
Beginning balance at Jun. 30, 2022	763,000	861,000	(86,000)	(12,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock based compensation expense		17,000
Net income	77,000		77,000
Repurchase of common stock			1,000
Awards effectively repurchased for required employee withholding taxes			(7,000)
Other comprehensive income/(loss)	7,000			7,000
Ending balance at Sep. 30, 2022	$ 856,000	$ 878,000	$ (17,000)	$ (5,000)