Fair Value measurements - Summary of Carrying Values and Associated Fair Values of Financial Assets and Liabilities (Details) - 5.75% Senior Notes Due 2028 - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Level 2
Financial assets:
Senior Notes	$ 313,287	$ 320,013
Carrying Value
Financial assets:
Senior Notes	$ 300,000	$ 300,000

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

No definition available.

Name:	us-gaap_LongTermDebtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant