Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Property, plant and equipment
Land	$ 8,287	$ 8,287
Building improvements	664,364	654,585
Capitalized leases for machinery, equipment and buildings	62,148	30,648
Property, plant and equipment, gross	734,799	693,520
Accumulated depreciation and amortization	(524,315)	(514,509)
Property Plant and Equipment Net before Construction in Progress	210,484	179,011
Construction in Progress	10,464	16,988
Property, plant and equipment, net	$ 220,948	$ 195,999