Lease Obligations (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) renewal	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Rent expense	$ 15,809	$ 14,899	$ 13,232
Implicit interest rate	6.93%	6.93%
Rock Hill Facility
Number of lease renewal terms | renewal	2
Lease renewal terms	5 years
Payment of base rent in 2019 through 2020	$ 710
Payment of base rent in 2021	$ 723
Minimum | Other Capital Lease Obligations
Implicit interest rate	1.75%	1.75%
Maximum | Other Capital Lease Obligations
Implicit interest rate	8.06%	8.06%