CONSOLIDATED STATEMENTS OF OPERATIONS & COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jul. 01, 2018	Jun. 30, 2019	Jul. 01, 2018
Revenue from services	$ 588,594	$ 614,301	$ 1,140,946	$ 1,168,689
Cost of services	430,277	448,717	834,253	859,837
Gross profit	158,317	165,584	306,693	308,852
Selling, general and administrative expense	127,599	134,207	257,260	259,970
Depreciation and amortization	9,827	10,101	19,779	20,191
Income from operations	20,891	21,276	29,654	28,691
Interest expense	(660)	(1,355)	(1,382)	(2,245)
Interest and other income	1,487	387	2,762	3,481
Interest and other income (expense), net	827	(968)	1,380	1,236
Income before tax expense	21,718	20,308	31,034	29,927
Income tax expense	2,312	2,576	3,352	3,440
Net income	$ 19,406	$ 17,732	$ 27,682	$ 26,487
Net income per common share:
Basic (in dollars per share)	$ 0.50	$ 0.44	$ 0.71	$ 0.66
Diluted (in dollars per share)	$ 0.49	$ 0.44	$ 0.70	$ 0.65
Weighted average shares outstanding:
Basic (in shares)	39,163	40,227	39,264	40,335
Diluted (in shares)	39,554	40,469	39,619	40,576
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Comprehensive income	$ 18,713	$ 15,811	$ 28,315	$ 23,182
Accumulated other comprehensive loss
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Foreign currency translation adjustment	$ (693)	$ (1,921)	$ 633	$ (3,305)