Property, Plant and Equipment (Details) - USD ($) $ in Thousands		Sep. 30, 2018	Dec. 31, 2017
Property, plant and equipment
Land		$ 9,082	$ 9,408
Building improvements		583,459	554,160
Capitalized leases for machinery, equipment and buildings		109,042	82,753
Property, plant and equipment, gross		701,583	646,321
Accumulated depreciation and amortization	[1]	(474,431)	(448,001)
Property Plant and Equipment Net before Construction in Progress		227,152	198,320
Construction in Progress		58,719	56,417
Property, plant and equipment, net		$ 285,871	$ 254,737

[1] Includes $44.9 million and $28.2 million of accumulated amortization related to assets under capital leases at September 30, 2018 and December 31, 2017, respectively.