Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Property, plant and equipment
Land	$ 9,417	$ 7,878
Building improvements	655,366	650,480
Capitalized leases for machinery, equipment and buildings	64,221	54,968
Property, plant and equipment, gross	729,004	713,326
Accumulated depreciation and amortization	(538,260)	(524,806)
Property Plant and Equipment Net before Construction in Progress	190,744	188,520
Construction in Progress	36,994	28,276
Property, plant and equipment, net	$ 227,738	$ 216,796