Significant Accounting Policies - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2022 USD ($) payment reportingUnit category	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Significant Accounting Policies Line Items [Line Items]
Maximum maturity duration for short term investment grouping	12 months
Number of payments missed for insured loans | payment	2
Number of reporting units | reportingUnit	1
Depreciation and amortization expense	$ 15.2	$ 15.9	$ 18.3
Minimum
Significant Accounting Policies Line Items [Line Items]
Number of payments missed for insured loans | payment	2
Useful life	3 years
Maximum
Significant Accounting Policies Line Items [Line Items]
Term of contract	12 months
Useful life	7 years
Mortgage
Significant Accounting Policies Line Items [Line Items]
Number of mortgage insurance product categories | category	2
Premium receivable for deferred monthly premiums	$ 32.0	30.3
Contractual deferred monthly premiums	$ 77.1	$ 74.0