Employee Benefits - Multiemployer Plans (Details) (Multiemployer Plans, Pension, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
International Union of Operating Engineers-Employers Construction Industry Retirement Plan
Multiemployer Plans [Line Items]
Contributions	$ 1,295	$ 534	$ 486
Expiration of Collective Bargaining Agreement	Dec. 31, 2015
Associated General Contractors of Washington Carpenter, Piledrivers, and Millwrights
Multiemployer Plans [Line Items]
Contributions	737	438	400
Expiration of Collective Bargaining Agreement	Dec. 31, 2015
Alaska Carpenters Trust Fund
Multiemployer Plans [Line Items]
Contributions	1,044	856	142
Expiration of Collective Bargaining Agreement	Dec. 31, 2017
Alaska Laborers Trust Fund [Member]
Multiemployer Plans [Line Items]
Contributions	$ 246	$ 52	$ 0
Expiration of Collective Bargaining Agreement	Dec. 31, 2015