Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Property, plant and equipment
Land	$ 9,417	$ 7,878
Building improvements	670,375	650,480
Capitalized leases for machinery, equipment and buildings	71,624	54,968
Property, plant and equipment, gross	751,416	713,326
Accumulated depreciation and amortization	(546,212)	(524,806)
Property Plant and Equipment Net before Construction in Progress	205,204	188,520
Construction in Progress	29,854	28,276
Property, plant and equipment, net	$ 235,058	$ 216,796