Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Property, plant and equipment
Land	$ 8,286	$ 1,752
Building improvements	689,520	647,181
Capitalized leases for machinery, equipment and buildings	26,338	28,680
Property, plant and equipment, gross	724,144	677,613
Accumulated depreciation and amortization	(491,356)	(464,852)
Property Plant and Equipment Net before Construction in Progress	232,788	212,761
Construction in Progress	21,786	15,150
Property, plant and equipment, net	$ 254,574	$ 227,911