Stock-Based Compensation - Summary of Nonvested Restricted Stock Awards and PSU Activity (Detail)	6 Months Ended
	Jun. 30, 2021 $ / shares shares
Time-Based Restricted Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Unvested shares of restricted stock and PSUs outstanding at beginning of period | shares	559,800
Restricted Stock Awards and PSUs, Granted | shares	133,100
Restricted Stock Awards and PSUs, Vested | shares	(274,000.0)
Restricted Stock Awards and PSUs, Forfeited | shares	(27,300)
Unvested shares of restricted stock and PSUs outstanding at end of period | shares	391,600
Unvested shares of restricted stock and PSUs outstanding, Weighted Average Grant Date Fair Value, at beginning of period | $ / shares	$ 156.48
Granted, Weighted Average Grant Date Fair Value | $ / shares	425.11
Vested, Weighted Average Grant Date Fair Value | $ / shares	131.63
Forfeited, Weighted Average Grant Date Fair Value | $ / shares	265.92
Unvested shares of restricted stock and PSUs outstanding, Weighted Average Grant Date Fair Value, at end of period | $ / shares	$ 257.56
Market-Based Restricted Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Unvested shares of restricted stock and PSUs outstanding at beginning of period | shares	1,748,500
Restricted Stock Awards and PSUs, Granted | shares	42,900
Restricted Stock Awards and PSUs, Forfeited | shares	(3,300)
Unvested shares of restricted stock and PSUs outstanding at end of period | shares	1,788,100
Unvested shares of restricted stock and PSUs outstanding, Weighted Average Grant Date Fair Value, at beginning of period | $ / shares	$ 115.91
Granted, Weighted Average Grant Date Fair Value | $ / shares	331.35
Forfeited, Weighted Average Grant Date Fair Value | $ / shares	331.35
Unvested shares of restricted stock and PSUs outstanding, Weighted Average Grant Date Fair Value, at end of period | $ / shares	$ 120.68
Performance-Based Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Restricted Stock Awards and PSUs, Granted | shares	57,900
Restricted Stock Awards and PSUs, Forfeited | shares	(20,800)
Unvested shares of restricted stock and PSUs outstanding at end of period | shares	37,100	[1]
Granted, Weighted Average Grant Date Fair Value | $ / shares	$ 564.68
Forfeited, Weighted Average Grant Date Fair Value | $ / shares	579.30
Unvested shares of restricted stock and PSUs outstanding, Weighted Average Grant Date Fair Value, at end of period | $ / shares	$ 556.50	[1]

[1] A maximum of 92,814 units could be awarded based upon Paycom’s Relative TSR over the applicable performance periods.