CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Revenue	$ 366,717,000	$ 324,315,000	$ 707,971,000	$ 627,095,000
Direct costs	235,053,000	206,565,000	451,002,000	395,391,000
Operating costs and expenses:
Indirect and selling expenses	101,450,000	90,410,000	197,969,000	180,069,000
Depreciation and amortization	5,595,000	4,045,000	10,357,000	8,514,000
Amortization of intangible assets	2,077,000	2,270,000	4,212,000	4,514,000
Total operating costs and expenses	109,122,000	96,725,000	212,538,000	193,097,000
Operating income	22,542,000	21,025,000	44,431,000	38,607,000
Interest expense	(2,934,000)	(2,167,000)	(5,387,000)	(3,833,000)
Other income (expense)	186,000	(318,000)	(226,000)	(214,000)
Income before income taxes	19,794,000	18,540,000	38,818,000	34,560,000
Provision for income taxes	5,183,000	4,923,000	8,889,000	8,526,000
Net income	$ 14,611,000	$ 13,617,000	$ 29,929,000	$ 26,034,000
Earnings per Share:
Basic	$ 0.78	$ 0.72	$ 1.59	$ 1.39
Diluted	$ 0.76	$ 0.71	$ 1.56	$ 1.36
Weighted-average Shares:
Basic	18,805	18,806	18,815	18,738
Diluted	19,133	19,209	19,213	19,208
Cash dividends declared per common share	$ 0.14	$ 0.14	$ 0.28	$ 0.28
Other comprehensive loss, net of tax	$ (2,853,000)	$ (3,317,000)	$ (2,570,000)	$ (1,708,000)
Comprehensive income, net of tax	$ 11,758,000	$ 10,300,000	$ 27,359,000	$ 24,326,000