UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended				9 Months Ended		12 Months Ended
	Sep. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Cash flows from operating activities:
Net income	$ 20,168	$ 13,261	$ 18,763	$ 9,106	$ 54,617	$ 37,754
Adjustments to reconcile net income to cash provided by operating activities:
Deferred income tax provision, net					302	(4,414)
Provision for credit losses					(139)	2,723
Depreciation and amortization					3,420	4,081
Stock-based compensation expense					10,448	8,707
Defined benefit pension plan expense					2,157	632
(Gain) loss on disposal or impairment of assets					(1,979)	1,795
Noncash lease expense					3,992	4,392
Loss on equity method investment					1,709	1,237
Other					681	820
Increase in operating assets
Trade receivables, net					(41,397)	(15,085)
Other assets					(6,384)	(5,034)
Increase in operating liabilities
Accrued payroll costs					7,715	31,496
Other liabilities					24,801	24,767
Cash provided by operating activities					59,943	93,871
Cash flows from investing activities:
Capital expenditures					(5,026)	(5,296)
Equity method investment					(7,000)	(2,500)
Proceeds from the sale of assets held within the Rabbi Trust					0	3,548
Net proceeds from the sale of assets					23,742	0
Cash provided by (used in) investing activities					11,716	(4,248)
Cash flows from financing activities:
Proceeds from credit facility					0	35,000
Repurchases of common stock					(44,407)	(29,623)
Cash dividends					(14,836)	(12,619)
Payments on other financing arrangements					(271)	(939)
Cash used in financing activities					(59,514)	(8,181)
Change in cash and cash equivalents					12,145	81,442
Cash and cash equivalents, beginning of period		103,486		19,831	103,486	19,831	$ 19,831
Cash and cash equivalents, end of period	115,631		101,273		115,631	101,273	$ 103,486
Cash Paid During the Period For:
Income taxes					17,845	13,493
Operating lease liabilities					5,591	5,641
Interest, net					1,934	1,924
Non-Cash Investing and Financing Transactions:
ROU assets obtained from operating leases					4,053	5,722
Employee stock purchase plan	$ 193	$ 170	$ 135	$ 142	$ 558	$ 411