Property, Plant and Equipment (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Property, plant and equipment
Land		$ 10,082	$ 9,408
Building improvements		611,399	554,160
Capitalized leases for machinery, equipment and buildings		107,445	82,753
Property, plant and equipment, gross		728,926	646,321
Accumulated depreciation and amortization	[1]	(486,371)	(448,001)
Property Plant and Equipment Net before Construction in Progress		242,555	198,320
Construction in Progress		55,896	56,417
Property, plant and equipment, net		$ 298,451	$ 254,737

[1] Includes $44.2 million and $28.2 million of accumulated amortization related to assets under capital leases at September 30, 2018 and December 31, 2017, respectively.