Fair Value of Financial Instruments and Concentrations of Credit Risk - Allowances for Losses on Accounts Receivable (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of year	$ 10,034	$ 9,457	$ 8,849
Provision for doubtful accounts	1,792	2,849	1,481
Write-offs, net of recoveries	(5,819)	(2,272)	(873)
Balance at end of year	$ 6,007	$ 10,034	$ 9,457