Unearned Revenue - Schedule of Unearned Revenue (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jun. 30, 2018	Jan. 01, 2018
Deferred Revenue Arrangement [Line Items]
Unearned revenue	$ 3,063,425	$ 3,416,340	$ 3,583,849
Transportation [Member]
Deferred Revenue Arrangement [Line Items]
Unearned revenue	2,311,712	2,594,464	2,858,747
Water [Member]
Deferred Revenue Arrangement [Line Items]
Unearned revenue	250,157	275,932	78,406
Specialty [Member]
Deferred Revenue Arrangement [Line Items]
Unearned revenue	501,556	545,944	646,696
California [Member]
Deferred Revenue Arrangement [Line Items]
Unearned revenue	360,822	397,338	406,056
California [Member] | Transportation [Member]
Deferred Revenue Arrangement [Line Items]
Unearned revenue	299,242	332,252	299,552
California [Member] | Water [Member]
Deferred Revenue Arrangement [Line Items]
Unearned revenue	11,297	17,485	27,328
California [Member] | Specialty [Member]
Deferred Revenue Arrangement [Line Items]
Unearned revenue	50,283	47,601	79,176
Northwest [Member]
Deferred Revenue Arrangement [Line Items]
Unearned revenue	313,276	383,856	315,582
Northwest [Member] | Transportation [Member]
Deferred Revenue Arrangement [Line Items]
Unearned revenue	242,666	315,189	273,864
Northwest [Member] | Water [Member]
Deferred Revenue Arrangement [Line Items]
Unearned revenue	10	206	2,606
Northwest [Member] | Specialty [Member]
Deferred Revenue Arrangement [Line Items]
Unearned revenue	70,600	68,461	39,112
Heavy Civil [Member]
Deferred Revenue Arrangement [Line Items]
Unearned revenue	1,705,551	1,915,020	2,232,613
Heavy Civil [Member] | Transportation [Member]
Deferred Revenue Arrangement [Line Items]
Unearned revenue	1,678,637	1,882,806	2,194,430
Heavy Civil [Member] | Water [Member]
Deferred Revenue Arrangement [Line Items]
Unearned revenue	26,914	32,214	38,183
Heavy Civil [Member] | Specialty [Member]
Deferred Revenue Arrangement [Line Items]
Unearned revenue	0	0	0
Federal [Member]
Deferred Revenue Arrangement [Line Items]
Unearned revenue	145,506	161,099	167,170
Federal [Member] | Transportation [Member]
Deferred Revenue Arrangement [Line Items]
Unearned revenue	23	26	317
Federal [Member] | Water [Member]
Deferred Revenue Arrangement [Line Items]
Unearned revenue	0	0	4,212
Federal [Member] | Specialty [Member]
Deferred Revenue Arrangement [Line Items]
Unearned revenue	145,483	161,073	162,641
Midwest [Member]
Deferred Revenue Arrangement [Line Items]
Unearned revenue	326,739	333,625	458,312
Midwest [Member] | Transportation [Member]
Deferred Revenue Arrangement [Line Items]
Unearned revenue	91,144	64,191	90,584
Midwest [Member] | Water [Member]
Deferred Revenue Arrangement [Line Items]
Unearned revenue	405	625	1,961
Midwest [Member] | Specialty [Member]
Deferred Revenue Arrangement [Line Items]
Unearned revenue	235,190	268,809	365,767
Water and Mineral Services [Member]
Deferred Revenue Arrangement [Line Items]
Unearned revenue	211,531	225,402	4,116
Water and Mineral Services [Member] | Transportation [Member]
Deferred Revenue Arrangement [Line Items]
Unearned revenue	0	0	0
Water and Mineral Services [Member] | Water [Member]
Deferred Revenue Arrangement [Line Items]
Unearned revenue	211,531	225,402	4,116
Water and Mineral Services [Member] | Specialty [Member]
Deferred Revenue Arrangement [Line Items]
Unearned revenue	$ 0	$ 0	$ 0