Accounts Receivable - Financing Receivables (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables	$ 45,882	$ 28,683
Financing receivable scheduled to be received in excess of one year	29,470	15,191
Sales-type lease receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables	31,201	16,558
Trade receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables	$ 14,681	$ 12,125