Investments - Valuation Methodologies (Details) $ in Thousands	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)
Investment [Line Items]
Other investments	$ 15,913	$ 16,613	$ 12,488
Private equity funds
Investment [Line Items]
Other investments	5,836	5,911
Direct credit co-investments
Investment [Line Items]
Other investments	3,093	4,013	3,940
Direct equity co-investments
Investment [Line Items]
Other investments	$ 6,984	$ 6,689	$ 4,814
Adjusted net asset value | Minimum | Private equity funds
Investment [Line Items]
Range of and weighted-average inputs	0.038
Adjusted net asset value | Maximum | Private equity funds
Investment [Line Items]
Range of and weighted-average inputs	0.052
Selected market return | Adjusted net asset value | Weighted Average | Private equity funds
Investment [Line Items]
Range of and weighted-average inputs	0.047
Market yield | Discounted cash flow | Minimum | Direct credit co-investments
Investment [Line Items]
Range of and weighted-average inputs	0.102
Market yield | Discounted cash flow | Maximum | Direct credit co-investments
Investment [Line Items]
Range of and weighted-average inputs	0.115
Market yield | Discounted cash flow | Weighted Average | Direct credit co-investments
Investment [Line Items]
Range of and weighted-average inputs	0.107
EBITDA multiple | Market approach | Minimum | Direct credit co-investments
Investment [Line Items]
Range of and weighted-average inputs	10.25
EBITDA multiple | Market approach | Maximum | Direct credit co-investments
Investment [Line Items]
Range of and weighted-average inputs	12.75
EBITDA multiple | Market approach | Weighted Average | Direct credit co-investments
Investment [Line Items]
Range of and weighted-average inputs	11.2
Equity multiple | Market approach | Direct credit co-investments
Investment [Line Items]
Range of and weighted-average inputs	1.25
Equity multiple | Market approach | Weighted Average | Direct credit co-investments
Investment [Line Items]
Range of and weighted-average inputs	1.25