Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended										6 Months Ended		12 Months Ended
	Jan. 27, 2018	Oct. 28, 2017	Jul. 29, 2017	Apr. 29, 2017	Jan. 28, 2017	Oct. 29, 2016	Jul. 30, 2016	Apr. 23, 2016	Jan. 23, 2016	Oct. 24, 2015	Jan. 27, 2018	Jan. 28, 2017	Jul. 29, 2017	Jul. 30, 2016	Jul. 25, 2015
Quarterly Financial Information Disclosure [Abstract]
Contract revenues	$ 655,133	$ 756,215	$ 780,188	$ 786,338	$ 701,131	$ 799,223	$ 789,159	$ 664,645	$ 559,470	$ 659,268	$ 1,411,348	$ 1,500,355	$ 3,066,880	$ 2,672,542	$ 2,022,312
Costs of earned revenues, excluding depreciation and amortization	540,633	600,847	606,898	621,475	561,371	614,990	605,909	520,408	450,284	506,978	1,141,480	1,176,361	2,404,734	2,083,579	1,593,250
Gross profit	114,500	155,368	173,290	164,863	139,760	184,233	183,250	144,237	109,186	152,290
Net income	$ 40,059	$ 28,776	$ 43,708	$ 38,796	$ 23,663	$ 51,050	$ 49,360	$ 33,083	$ 15,473	$ 30,824	$ 68,835	$ 74,713	$ 157,217	$ 128,740	$ 84,324
Basic earnings per common share (in dollars per share)	$ 1.29	$ 0.93	$ 1.41	$ 1.24	$ 0.75	$ 1.62	$ 1.57	$ 1.02	$ 0.47	$ 0.94	$ 2.22	$ 2.37	$ 5.01	$ 3.98	$ 2.48
Diluted earnings per common share (in dollars per share)	$ 1.24	$ 0.90	$ 1.38	$ 1.22	$ 0.74	$ 1.59	$ 1.54	$ 1.00	$ 0.46	$ 0.91	$ 2.15	$ 2.32	$ 4.92	$ 3.89	$ 2.41