Employee Benefits (Tables)

12 Months Ended

Dec. 31, 2017

Compensation and Retirement Disclosure [Abstract]

Schedule of multiemployer plans

The following table presents the Company's participation in these plans:

		Pension Protection Act ("PPA") Certified Zone Status (1)		FIP/RP Status	Contributions							Expiration of Collective Bargaining Agreement
	Employer Identification Number										Surcharge Imposed
Pension Trust Fund		2017	2016	P/I (2)	2017		2016		2015
International Union of Operating Engineers - Employers Construction Industry Retirement Plan - Local 302 and 612 Trust Funds	91-6028571	Green	Green	N/A	$	1,974	$	2,158	$	1,518	—	2018
Associated General Contractors of Washington Carpenter, Piledrivers, and Millwrights	91-6029051 91-6029049	Green	Green	N/A	$	693	$	938	$	748	—	2018
Alaska Carpenters Trust Fund	92-0120866	Green	Green	N/A	$	396	$	889	$	807	—	2020
Alaska Laborers Trust Fund	91-6028298	Yellow	Yellow	P	$	218	$	126	$	110	—	2017

(1) The most recent PPA zone status available in 2017 and 2016 is for the plan's year end during 2016 and 2015, respectively. Zone status is based on information received from the plan and is indicative of the plans funding status. Among other factors, plans in the red zone are generally less than 65 percent funded, plans in the orange zone are less than 80 percent funded and have an Accumulated Funding Deficiency in the current year or projected into the next six years, plans in the yellow zone are less than 80 percent funded, and plans in the green zone are at least 80 percent funded.

(2) The FIP/RP Status P/I column indicates plans for which a financial improvement plan ("FIP") or a rehabilitation plan ("RP") is either pending ("P"), or implemented ("I").