Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended										6 Months Ended		12 Months Ended
	Jan. 26, 2019	Oct. 27, 2018	Jul. 28, 2018	Apr. 28, 2018	Jan. 27, 2018	Oct. 28, 2017	Jul. 29, 2017	Apr. 29, 2017	Jan. 28, 2017	Oct. 29, 2016	Jan. 27, 2018	Jan. 28, 2017	Jan. 26, 2019	Jul. 29, 2017	Jul. 30, 2016
Quarterly Financial Information Disclosure [Abstract]
Contract revenues	$ 748,619	$ 848,237	$ 799,470	$ 731,375	$ 655,133	$ 756,215	$ 780,188	$ 786,338	$ 701,131	$ 799,223	$ 1,411,348	$ 1,500,355	$ 3,127,700	$ 3,066,880	$ 2,672,542
Costs of earned revenues, excluding depreciation and amortization	633,279	687,164	642,376	599,573	540,633	600,847	606,898	621,475	561,371	614,990	1,141,480	1,176,361	2,562,392	2,404,734	2,083,579
Gross profit	115,340	161,073	157,094	131,802	114,500	155,368	173,290	164,863	139,760	184,233
Net income	$ (12,054)	$ 27,830	$ 29,900	$ 17,231	$ 40,059	$ 28,776	$ 43,708	$ 38,796	$ 23,663	$ 51,050	$ 68,835	$ 74,713	$ 62,907	$ 157,217	$ 128,740
Basic earnings per common share (in dollars per share)	$ (0.38)	$ 0.89	$ 0.96	$ 0.55	$ 1.29	$ 0.93	$ 1.41	$ 1.24	$ 0.75	$ 1.62	$ 2.22	$ 2.37	$ 2.01	$ 5.01	$ 3.98
Diluted earnings per common share (in dollars per share)	$ (0.38)	$ 0.87	$ 0.94	$ 0.53	$ 1.24	$ 0.90	$ 1.38	$ 1.22	$ 0.74	$ 1.59	$ 2.15	$ 2.32	$ 1.97	$ 4.92	$ 3.89