Borrowings and Debt - Long Term Debt (Details) - USD ($)	Dec. 31, 2024	Aug. 29, 2024	Dec. 31, 2023	Jul. 31, 2016
Debt Instrument [Line Items]
Carrying value	$ 275,000,000.0
Significant other observable inputs (Level II)
Debt Instrument [Line Items]
Carrying value	274,300,000		$ 273,900,000
Fair Value	271,700,000		263,100,000
Line of Credit | Revolving credit facility | Significant other observable inputs (Level II)
Debt Instrument [Line Items]
Carrying value	0		0
Fair Value	0		0
Line of Credit | Revolving credit facility | The Acadian Credit Agreement
Debt Instrument [Line Items]
Face amount	140,000,000
Maximum borrowing capacity		$ 140,000,000
Line of Credit | Revolving credit facility | The Acadian Credit Agreement | Significant other observable inputs (Level II)
Debt Instrument [Line Items]
Carrying value	0		0
Fair Value	0		0
Line of Credit | Revolving credit facility | The Original Credit Agreement
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 125,000,000
Senior notes | 4.80% Senior Notes Due July 27, 2026
Debt Instrument [Line Items]
Face amount	$ 275,000,000
Interest rate	4.80%			4.80%
Senior notes | 4.80% Senior Notes Due July 27, 2026 | Significant other observable inputs (Level II)
Debt Instrument [Line Items]
Carrying value	$ 274,300,000		273,900,000
Fair Value	$ 271,700,000		$ 263,100,000