Business Combinations - Asterion (Details) - USD ($) $ in Thousands	Apr. 10, 2018	Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Assets Acquired:
Goodwill		$ 609,458	$ 708,258	$ 747,325
Asterion
Business Combinations and Acquisitions
Purchase price	$ 19,500
Assets Acquired:
Cash and cash equivalents	5,595
Accounts receivable	25,740
Other current assets	2,282
Inventories, net	1,137
Property, plant, and equipment, net	4,747
Deferred income tax assets	6,316
Other noncurrent assets	522
Intangible assets, net	3,525
Goodwill	1,493
Total identifiable assets acquired	51,357
Liabilities Assumed:
Accounts payable	(5,596)
Income tax payable	(5)
Accrued liabilities	(6,593)
Accrued compensation and benefits	(7,079)
Deferred revenue	(880)
Current portion of long term debt	(994)
Customer deposits	(462)
Pension liabilities	(7,135)
Other long-term liabilities	(1,324)
Deferred income tax liabilities	(1,171)
Capital lease obligations, net of current maturities	(650)
Total liabilities assumed	(31,889)
Total Consideration	$ 19,468