Schedule II - Valuation and Qualifying Accounts (Details) - Allowance for doubtful accounts rollforward - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of year	$ 8,700	$ 8,000	$ 6,800
Additions: charges to costs and expenses	6,438	2,928	1,577
Deductions: write-offs	1,138	2,228	377
Balance at end of year	$ 14,000	$ 8,700	$ 8,000