Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								6 Months Ended		12 Months Ended
	Jan. 25, 2020	Oct. 26, 2019	Jul. 27, 2019	Apr. 27, 2019	Jan. 26, 2019	Oct. 27, 2018	Jul. 28, 2018	Apr. 28, 2018	Jan. 27, 2018	Jan. 28, 2017	Jan. 25, 2020	Jan. 26, 2019	Jul. 29, 2017
Quarterly Financial Information Disclosure [Abstract]
Contract revenues	$ 737,603	$ 884,115	$ 884,221	$ 833,743	$ 748,619	$ 848,237	$ 799,470	$ 731,375	$ 1,411,348	$ 1,500,355	$ 3,339,682	$ 3,127,700	$ 3,066,880
Costs of earned revenues, excluding depreciation and amortization	633,203	724,378	720,382	701,767	633,279	687,164	642,376	599,573	1,141,480	1,176,361	2,779,730	2,562,392	2,404,734
Gross profit	104,400	159,737	163,839	131,976	115,340	161,073	157,094	131,802
Net income	$ (11,189)	$ 24,229	$ 29,896	$ 14,279	$ (12,054)	$ 27,830	$ 29,900	$ 17,231	$ 68,835	$ 74,713	$ 57,215	$ 62,907	$ 157,217
Basic earnings per common share (in dollars per share)	$ (0.35)	$ 0.77	$ 0.95	$ 0.45	$ (0.38)	$ 0.89	$ 0.96	$ 0.55	$ 2.22	$ 2.37	$ 1.82	$ 2.01	$ 5.01
Diluted earnings per common share (in dollars per share)	$ (0.35)	$ 0.76	$ 0.94	$ 0.45	$ (0.38)	$ 0.87	$ 0.94	$ 0.53	$ 2.15	$ 2.32	$ 1.80	$ 1.97	$ 4.92