Accounts Receivable Sales Agreement (Details) - USD ($) $ in Thousands		6 Months Ended
	Jul. 13, 2021	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 13, 2019
Accounts Receivable Sales Agreement
Cash and cash equivalents		$ 399,881	$ 472,246	$ 484,336	$ 435,990
5.50% senior notes due January 2023
Accounts Receivable Sales Agreement
Interest rate (as a percent)		5.50%
Accounts Receivable Sales Agreement
Accounts Receivable Sales Agreement
Agreement amount	$ 150,000					$ 250,000
Agreement expiration term extension (in years)	2 years
Accounts receivables sold to purchasers		$ 84,000	54,000
Gain (loss) on sale of receivables		0
Trade receivables pledged as collateral		$ 40,900	$ 63,100
Accounts Receivable Sales Agreement | Maximum | Forecast
Accounts Receivable Sales Agreement
Possible amount that the agreement could be increased	$ 200,000
Acceleration Of Expiration [Member] | 5.50% senior notes due January 2023
Accounts Receivable Sales Agreement
Interest rate (as a percent)		5.50%
Acceleration Of Expiration [Member] | Minimum | Forecast
Accounts Receivable Sales Agreement
Cash and cash equivalents	$ 220,000