Investments - Other Investments, at Fair Value (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2016 USD ($) fund	Dec. 31, 2015 USD ($)
Other Investments [Line Items]
Other investments, at fair value	$ 936,158	$ 1,034,032
Valuation lag period	3 months
Unfunded commitments	$ 138,400
Private equities and private equity funds
Other Investments [Line Items]
Other investments, at fair value	229,756	254,883
Unfunded commitments	138,400
Fixed income funds
Other Investments [Line Items]
Other investments, at fair value	248,815	291,736
Fixed income hedge funds
Other Investments [Line Items]
Other investments, at fair value	$ 111,543	109,400
Imposed lock-up period (up to) (years)	3 years
Number of days to give notice for quarterly hedge fund redemptions	60 days
Gates or side-pocket investments	$ 800
Equity funds
Other Investments [Line Items]
Other investments, at fair value	163,050	147,390
Multi-strategy hedge fund
Other Investments [Line Items]
Other investments, at fair value	$ 98,416	99,020
Number of days to give notice for quarterly hedge fund redemptions	60 days
Real estate debt fund
Other Investments [Line Items]
Other investments, at fair value	$ 0	54,829
Redemption request period (days)	10 days
CLO equities
Other Investments [Line Items]
Other investments, at fair value	$ 65,156	61,702
CLO equity funds
Other Investments [Line Items]
Other investments, at fair value	$ 13,513	13,928
Number of CLO equity funds | fund	2
Call options on equities
Other Investments [Line Items]
Other investments, at fair value	$ 4,850	0
Other
Other Investments [Line Items]
Other investments, at fair value	1,059	$ 1,144
CLO Equity Fund One
Other Investments [Line Items]
Other investments, at fair value	$ 3,600
CLO Equity Fund One | Minimum
Other Investments [Line Items]
CLO equity fund pay out period (years)	2 years
CLO Equity Fund One | Maximum
Other Investments [Line Items]
CLO equity fund pay out period (years)	6 years
CLO Equity Fund Two
Other Investments [Line Items]
Other investments, at fair value	$ 9,900