Summary of Significant Accounting Policies and Other Items - Depreciation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Depreciation expense
Total depreciation	$ 30,153	$ 23,271	$ 21,241
Cost of Sales | Product revenue
Depreciation expense
Depreciation - Cost of sales	3,262	3,169	2,869
Cost of Sales | Rental revenue
Depreciation expense
Depreciation - Cost of sales	17,997	14,912	15,121
Cost of Sales | Field service and other revenue
Depreciation expense
Depreciation - Cost of sales	8,456	4,786	2,659
Selling, General and Administrative Expenses
Depreciation expense
Depreciation - SG&A	$ 438	$ 404	$ 592