Property, Plant and Equipment (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Property, plant and equipment
Land	$ 2,010	$ 2,010
Building improvements	582,681	581,286
Machinery and equipment	370,381	360,199
Capitalized leases for machinery, equipment and buildings	28,270	35,129
Property, plant and equipment, gross	983,342	978,624
Accumulated depreciation and amortization	(333,470)	(313,067)
Property Plant and Equipment Net before Construction in Progress	649,872	665,557
Construction in Progress	17,824	18,303
Property, plant and equipment, net	$ 667,696	$ 683,860