Net Periodic Pension Cost (Details) - UNITED KINGDOM - Foreign Pension Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Components of the net periodic pension cost:
Interest cost	$ 1,340	$ 1,589	$ 1,403
Expected return on plan assets	(1,844)	(1,958)	(1,595)
Amortization of actuarial losses	875	374	668
Net periodic pension cost	$ 371	$ 5	$ 476