Summary of Accounting Policies - Labor Agreements and Cash and Cash Equivalents (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash deposits
Cash deposits with U.S. financial institutions in excess of federally insured limits	$ 0	$ 3,100
Cash and Cash Equivalents, at Carrying Value	53,629	53,133	$ 32,942	$ 18,161
Foreign subsidiaries
Cash deposits
Cash and Cash Equivalents, at Carrying Value	$ 45,100	$ 41,700
Labor force concentration risk | Collective bargaining agreements
Summary of Accounting Policies
Percentage of labor force covered	28.00%