Unearned Revenue - Schedule of Unearned Revenue (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018
Disaggregation Of Revenue [Line Items]
Unearned revenue	$ 3,692,312	$ 2,863,611	$ 3,416,340
California [Member]
Disaggregation Of Revenue [Line Items]
Unearned revenue	724,175	475,885	397,338
Northwest [Member]
Disaggregation Of Revenue [Line Items]
Unearned revenue	468,269	418,051	383,856
Heavy Civil [Member]
Disaggregation Of Revenue [Line Items]
Unearned revenue	1,763,965	1,328,691	1,915,020
Federal [Member]
Disaggregation Of Revenue [Line Items]
Unearned revenue	147,946	137,611	161,099
Midwest [Member]
Disaggregation Of Revenue [Line Items]
Unearned revenue	363,237	309,459	333,625
Water and Mineral Services [Member]
Disaggregation Of Revenue [Line Items]
Unearned revenue	224,720	193,914	225,402
Transportation [Member]
Disaggregation Of Revenue [Line Items]
Unearned revenue	2,921,437	2,187,300	2,594,464
Transportation [Member] | California [Member]
Disaggregation Of Revenue [Line Items]
Unearned revenue	590,641	402,482	332,252
Transportation [Member] | Northwest [Member]
Disaggregation Of Revenue [Line Items]
Unearned revenue	374,148	344,414	315,189
Transportation [Member] | Heavy Civil [Member]
Disaggregation Of Revenue [Line Items]
Unearned revenue	1,751,819	1,311,518	1,882,806
Transportation [Member] | Federal [Member]
Disaggregation Of Revenue [Line Items]
Unearned revenue	80	19	26
Transportation [Member] | Midwest [Member]
Disaggregation Of Revenue [Line Items]
Unearned revenue	204,749	128,867	64,191
Transportation [Member] | Water and Mineral Services [Member]
Disaggregation Of Revenue [Line Items]
Unearned revenue	0	0	0
Water [Member]
Disaggregation Of Revenue [Line Items]
Unearned revenue	253,418	220,303	275,932
Water [Member] | California [Member]
Disaggregation Of Revenue [Line Items]
Unearned revenue	14,382	7,314	17,485
Water [Member] | Northwest [Member]
Disaggregation Of Revenue [Line Items]
Unearned revenue	710	1,759	206
Water [Member] | Heavy Civil [Member]
Disaggregation Of Revenue [Line Items]
Unearned revenue	12,146	17,173	32,214
Water [Member] | Federal [Member]
Disaggregation Of Revenue [Line Items]
Unearned revenue	1,350	0	0
Water [Member] | Midwest [Member]
Disaggregation Of Revenue [Line Items]
Unearned revenue	110	143	625
Water [Member] | Water and Mineral Services [Member]
Disaggregation Of Revenue [Line Items]
Unearned revenue	224,720	193,914	225,402
Specialty [Member]
Disaggregation Of Revenue [Line Items]
Unearned revenue	517,457	456,008	545,944
Specialty [Member] | California [Member]
Disaggregation Of Revenue [Line Items]
Unearned revenue	119,152	66,089	47,601
Specialty [Member] | Northwest [Member]
Disaggregation Of Revenue [Line Items]
Unearned revenue	93,411	71,878	68,461
Specialty [Member] | Heavy Civil [Member]
Disaggregation Of Revenue [Line Items]
Unearned revenue	0	0	0
Specialty [Member] | Federal [Member]
Disaggregation Of Revenue [Line Items]
Unearned revenue	146,516	137,592	161,073
Specialty [Member] | Midwest [Member]
Disaggregation Of Revenue [Line Items]
Unearned revenue	158,378	180,449	268,809
Specialty [Member] | Water and Mineral Services [Member]
Disaggregation Of Revenue [Line Items]
Unearned revenue	$ 0	$ 0	$ 0