Long-Lived Assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Property, plant and equipment
Property, plant and equipment cost	$ 961,009		$ 937,927
Less accumulated depreciation	378,738		358,820
Total property, plant and equipment, net	582,271		$ 579,107
Depreciation expense	$ 21,400	$ 20,700