Revenue Recognition - Contract Balances with Customers (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Trade accounts receivable and contract assets, net:
Trade accounts receivable	$ 166,455		$ 166,455		$ 156,648
Contract assets	43,896		43,896		63,758
Allowance for doubtful accounts	(19,401)		(19,401)		(23,777)
Total trade accounts receivable and contract assets, net	190,950		190,950		196,629
Contract liabilities:
Current	89,622		89,622		101,060
Noncurrent	11,663		11,663		10,572
Total contract liabilities	101,285		101,285		111,632
Revenue recognized	3,794	$ 19,490	63,581	$ 67,263
Sales and services
Trade accounts receivable and contract assets, net:
Trade accounts receivable	162,390		162,390		152,632
Leasing
Trade accounts receivable and contract assets, net:
Trade accounts receivable	$ 4,065		$ 4,065		$ 4,016