Employee Benefit Plans - Additional Information (Details) - USD ($) $ / shares in Units, shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accrued matching contribution	$ 1,800,000	$ 1,600,000
Kforce common stock held by both plans (in shares)	146	167
Employee stock purchase plan (in shares)	19	25	34
Current deferred compensation liability	$ 1,800,000	$ 2,900,000
Deferred compensation plan	28,900,000	28,900,000
Compensation expenses (income)	876,000	722,000	$ 881,000
Deferred compensation plan assets	29,100,000	31,400,000
Life insurance	213,100,000
Gains (losses) attributable to the investments in bond mutual funds	$ 0	0	$ 0
Normal retirement age	65 years
Early retirement age	55 years
Vesting percentage under plan for attaining age 55 and 10 years	100.00%
Defined benefit plan arrangement minimum age	55 years
Completed at least credited service period	10 years
Vesting percentage under plan prior to attaining age 55 and 10 years	0.00%
Defined benefit plan employees minimum requisition period under specific conditions	5 years
Benefits payable targeted percentage	45.00%
Period in which the executive officer earned the highest salary and bonus	3 years
Employment period for computation of benefit	10 years
Eligible age under condition one for reduced benefits under the plan	62 years
Eligible service under condition one for reduced benefits under plan	10 years
Eligible age under condition two for reduced benefits under plan	55 years
Eligible service under condition two for reduced benefits under plan	25 years
Lump sum payment period	10 years
Payment to participants under the SERP	$ 0	0
Accumulated benefit obligation	15,000,000.0	$ 14,300,000
Employer contributions to benefit plans	0
Expected future benefit payments, next twelve months	$ 0
ESPP
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percentage of discount on shares purchased under employee stock purchase plan	5.00%
Average purchase price (in dollars per share)	$ 28.93	$ 20.65	$ 19.37