Summary of Significant Accounting Policies - Fair Value Measurements - Debt (Details) $ in Millions	Dec. 31, 2020 USD ($)
Level 1 \| Senior Notes \| 4.400% Senior Notes due 2024
Debt
Fair value of debt	$ 381.7
Level 2 \| Unsecured Debt \| 2017 Credit Agreement, senior unsecured term loan facility
Debt
Fair value of debt	$ 263.1

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