Property, Plant and Equipment (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Property, plant and equipment
Land	$ 1,764	$ 1,764
Building improvements	872,575	855,318
Capitalized leases for machinery, equipment and buildings	25,680	16,133
Property, plant and equipment, gross	900,019	873,215
Accumulated depreciation and amortization	(429,904)	(395,520)
Property Plant and Equipment Net before Construction in Progress	470,115	477,695
Construction in Progress	12,672	8,578
Property, plant and equipment, net	$ 482,787	$ 486,273