Consolidated Statements of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Statement of Comprehensive Income [Abstract]
Revenue	$ 1,104,925	$ 963,897	$ 948,424
Operating expenses	945,635	825,351	823,496
Gross margin	159,290	138,546	124,928
Corporate general and administrative expenses	56,150	46,066	44,406
Legal settlement, net	30,468	0	0
Operating income (loss)	72,672	92,480	80,522
Other income (expense):
Interest expense	(3,868)	(4,983)	(5,765)
Gain (loss) on sale of operations, net	5,995	(509)	417
Other income, net	18,241	16,500	17,715
Total other income, net	20,368	11,008	12,367
Income from continuing operations before income tax expense	93,040	103,488	92,889
Income tax expense	22,129	25,141	21,840
Income from continuing operations	70,911	78,347	71,049
Loss from operations of discontinued operations, net of tax	(24)	(48)	(335)
Net income	$ 70,887	$ 78,299	$ 70,714
Basic:
Continuing operations (in dollars per share)	$ 1.35	$ 1.44	$ 1.31
Discontinued operations (in dollars per share)	0	0	(0.01)
Net income (loss) (in dollars per share)	1.35	1.44	1.30
Diluted:
Continuing operations (in dollars per share)	1.32	1.42	1.27
Discontinued operations (in dollars per share)	0	(0.01)	(0.01)
Net income (loss) (in dollars per share)	$ 1.32	$ 1.41	$ 1.26
Basic weighted average common shares outstanding (in shares)	52,637	54,288	54,299
Diluted weighted average common shares outstanding (in shares)	53,723	55,359	55,895
Comprehensive income:
Net income	$ 70,887	$ 78,299	$ 70,714
Other comprehensive income:
Net unrealized (loss) gain on available-for-sale securities, net of income tax (benefit) expense of $(179), $(14) and $351	(478)	(42)	940
Net unrealized gain (loss) on interest rate swaps, net of income tax expense (benefit) of $577, $(494) and $(380)	1,799	(1,525)	(1,222)
Foreign currency translation	(19)	(22)	(17)
Total other comprehensive income (loss)	1,302	(1,589)	(299)
Total comprehensive income	$ 72,189	$ 76,710	$ 70,415