Employee Benefit Plans (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) participant	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Employee Benefits Plans [Line Items]
Defined Contribution Plan, Maximum Annual Contribution Per Employee, Percent	50.00%
Defined Contribution Plan, Employer Matching Contribution, Percent	6.00%
Defined Contribution Plan, Cost	$ 12,100	$ 11,000	$ 5,400
Number of Participants in Non Qualifed Deferred Compensation Plan | participant	61
Deferred Compensation Liability, Current and Noncurrent	$ 24,700	21,500
Multiemployer Plan, Contributions by Employer	$ 36,784	33,082	28,559
Multiemployer Plans, Maximum Percent Funded Status for Red Zone	65.00%
Multiemployer Plans, Maximum Percent Funded Status for Yellow Zone and Minmum Percent for Green Zone	80.00%
Locals 302 and 612 Operating Engineers Employers Retirement Fund [Member]
Employee Benefits Plans [Line Items]
Multiemployer Plan, Contributions by Employer	$ 3,646	3,113	3,000
Operating Engineers Pension Trust Fund [Member]
Employee Benefits Plans [Line Items]
Multiemployer Plan, Contributions by Employer	4,692	5,357	3,647
Pension Trust Fund for Operating Engineers Pension Plan [Member]
Employee Benefits Plans [Line Items]
Multiemployer Plan, Contributions by Employer	10,431	9,266	9,070
Laborers Pension Trust Fund for Northern California [Member] [Member]
Employee Benefits Plans [Line Items]
Multiemployer Plan, Contributions by Employer	2,464	2,215	2,403
Laborers Pension Trust Fund for Northern California [Member] [Member] [Member]
Employee Benefits Plans [Line Items]
Multiemployer Plan, Contributions by Employer	2,002	2,095	1,349
Laborers Pension Fund [Member]
Employee Benefits Plans [Line Items]
Multiemployer Plan, Contributions by Employer	3,208	2,328	1,919
All Other Pension Trust Funds [Member]
Employee Benefits Plans [Line Items]
Multiemployer Plan, Contributions by Employer	10,341	8,708	7,171
Deferred Profit Sharing [Member]
Employee Benefits Plans [Line Items]
Defined Contribution Plan, Cost	$ 0	$ 0	$ 0