Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Property, plant and equipment
Land	$ 8,287	$ 1,752
Building improvements	706,198	647,181
Capitalized leases for machinery, equipment and buildings	26,338	28,680
Property, plant and equipment, gross	740,823	677,613
Accumulated depreciation and amortization	(502,466)	(464,852)
Property Plant and Equipment Net before Construction in Progress	238,357	212,761
Construction in Progress	22,686	15,150
Property, plant and equipment, net	$ 261,043	$ 227,911