Retirement Plans - Multiemployer Pension (Details) - Multiemployer Plans, Pension - WAPA $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) item	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Multiemployer pension
Number of collective bargaining agreements | item	2
Renewal period after expiration	18 months
Period for payments under the plan (in years)	3 years
Maximum period for payments under the plan (in years)	10 years
Period for ending of payment obligation (in years)	20 years
Additional plan commitment period	5 years
Contribution to the plan assets (as a percent)		5.00%
Contributions | $	$ 156	$ 151	$ 144
Beginning on January 1, 2013
Multiemployer pension
Increase in the contribution rate agreed by the company under the "preferred schedule" of the Rehabilitation Plan (as a percent)	3.0
Beginning on January 1, 2014
Multiemployer pension
Increase in the contribution rate agreed by the company under the "preferred schedule" of the Rehabilitation Plan (as a percent)	3.0
Beginning on January 1, 2015
Multiemployer pension
Increase in the contribution rate agreed by the company under the "preferred schedule" of the Rehabilitation Plan (as a percent)	3
Starting January 1, 2016
Multiemployer pension
Increase in the contribution rate agreed by the company under the "preferred schedule" of the Rehabilitation Plan (as a percent)	3