UNAUDITED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Statement [Abstract]
Contract revenues	$ 649,573	$ 513,051	$ 1,242,059	$ 1,031,521
Contract costs	568,551	451,746	1,084,084	908,584
Gross profit	81,022	61,305	157,975	122,937
Selling, general and administrative expenses	51,890	41,199	101,537	86,245
Amortization of intangible assets	578	1,203	1,156	2,431
Gain on sale of property and equipment	(1,111)	(439)	(1,794)	(1,489)
Income from operations	29,665	19,342	57,076	35,750
Other income (expense):
Interest income	15	4	28	6
Interest expense	(678)	(1,315)	(1,153)	(2,828)
Other income (expense), net	80	321	121	(574)
Income before provision for income taxes	29,082	18,352	56,072	32,354
Income tax expense	7,863	4,967	14,925	9,037
Net income	$ 21,219	$ 13,385	$ 41,147	$ 23,317
Income per common share:
Basic (in dollars per share)	$ 1.26	$ 0.80	$ 2.45	$ 1.40
Diluted (in dollars per share)	$ 1.24	$ 0.80	$ 2.41	$ 1.39
Weighted average number of common shares and potential common shares outstanding:
Basic (in shares)	16,854	16,685	16,807	16,656
Diluted (in shares)	17,125	16,765	17,093	16,751
Net income	$ 21,219	$ 13,385	$ 41,147	$ 23,317
Other comprehensive income (loss):
Foreign currency translation adjustment	413	(39)	666	48
Other comprehensive income (loss):	413	(39)	666	48
Total comprehensive income	$ 21,632	$ 13,346	$ 41,813	$ 23,365