Business Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Revenue from external customers	$ 801,274	$ 957,126	$ 762,913	$ 468,400	$ 666,681	$ 803,905	$ 604,579	$ 439,452	$ 2,989,713	$ 2,514,617	$ 2,371,029
Gross profit	100,707	114,530	74,570	25,126	81,250	107,674	73,201	39,245	314,933	301,370	299,836
Segment assets	1,871,978				1,733,453				1,871,978	1,733,453	1,626,878
Reconciliation from Segment Totals to Consolidated [Abstract]
Cash and cash equivalents	233,711				189,326				233,711	189,326	252,836	$ 255,961
Receivables, net	479,791				419,345				479,791	419,345
Other current assets	36,513				39,908				36,513	39,908
Property and equipment, net	407,418				406,650				407,418	406,650
Investments in affiliates	38,469				35,668				38,469	35,668	33,182
Other noncurrent assets	75,199				85,449				75,199	85,449
Gross profit	100,707	$ 114,530	$ 74,570	$ 25,126	81,250	$ 107,674	$ 73,201	$ 39,245	314,933	301,370	299,836
Selling, general and administrative expenses									222,811	219,299	203,817
Restructuring gains									(2,411)	(1,925)	(6,003)
Total Other Income (Expense)									(5,748)	(4,008)	6,881
Income before provision for income taxes									104,463	96,362	103,427
Gain on sales of property and equipment									(4,182)	(8,358)	(8,286)
Construction [Member]
Segment Reporting Information [Line Items]
Revenue from external customers									1,664,708	1,365,198	1,262,675
Large Project Construction [Member]
Segment Reporting Information [Line Items]
Revenue from external customers									1,032,229	888,193	812,720
Construction Materials [Member]
Segment Reporting Information [Line Items]
Revenue from external customers									292,776	261,226	295,634
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues									3,164,077	2,678,420	2,507,679
Gross profit									314,933	301,370	299,836
Depreciation, depletion and amortization									55,997	53,049	52,849
Segment assets	758,845				748,770				758,845	748,770	703,274
Reconciliation from Segment Totals to Consolidated [Abstract]
Gross profit									314,933	301,370	299,836
Operating Segments [Member] | Construction [Member]
Segment Reporting Information [Line Items]
Revenue from external customers									1,664,708	1,365,198	1,262,675
Gross profit									247,014	209,215	187,506
Depreciation, depletion and amortization									22,517	22,816	20,117
Segment assets	136,031				151,475				136,031	151,475	139,399
Reconciliation from Segment Totals to Consolidated [Abstract]
Gross profit									247,014	209,215	187,506
Operating Segments [Member] | Large Project Construction [Member]
Segment Reporting Information [Line Items]
Revenue from external customers									1,032,229	888,193	812,720
Gross profit									29,793	64,137	79,467
Depreciation, depletion and amortization									11,087	6,796	10,343
Segment assets	340,105				314,823				340,105	314,823	274,975
Reconciliation from Segment Totals to Consolidated [Abstract]
Gross profit									29,793	64,137	79,467
Operating Segments [Member] | Construction Materials [Member]
Segment Reporting Information [Line Items]
Revenues									467,140	425,029	432,284
Gross profit									38,126	28,018	32,863
Depreciation, depletion and amortization									22,393	23,437	22,389
Segment assets	282,709				282,472				282,709	282,472	288,900
Reconciliation from Segment Totals to Consolidated [Abstract]
Gross profit									38,126	28,018	32,863
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from external customers									(174,364)	(163,803)	(136,650)
Intersegment Eliminations [Member] | Construction [Member]
Segment Reporting Information [Line Items]
Revenue from external customers									0	0	0
Intersegment Eliminations [Member] | Large Project Construction [Member]
Segment Reporting Information [Line Items]
Revenue from external customers									0	0	0
Intersegment Eliminations [Member] | Construction Materials [Member]
Segment Reporting Information [Line Items]
Revenue from external customers									(174,364)	(163,803)	(136,650)
Segment Reconciling Items [Member]
Reconciliation from Segment Totals to Consolidated [Abstract]
Cash and cash equivalents	233,711				189,326				233,711	189,326	252,836
Short-term and long-term marketable securities	132,790				127,779				132,790	127,779	105,695
Receivables, net	479,791				419,345				479,791	419,345	340,822
Deferred income taxes	0				0				0	0	4,329
Other current assets	140,478				113,010				140,478	113,010	85,556
Property and equipment, net	29,242				32,397				29,242	32,397	36,721
Other noncurrent assets	$ 58,652				$ 67,158				$ 58,652	$ 67,158	$ 64,463