Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Property, plant and equipment
Land	$ 8,403	$ 7,878
Building improvements	649,030	650,480
Capitalized leases for machinery, equipment and buildings	63,775	54,968
Property, plant and equipment, gross	721,208	713,326
Accumulated depreciation and amortization	(531,480)	(524,806)
Property Plant and Equipment Net before Construction in Progress	189,728	188,520
Construction in Progress	32,889	28,276
Property, plant and equipment, net	$ 222,617	$ 216,796