Investments (Other investments) (Details) - USD ($) $ in Thousands		6 Months Ended	12 Months Ended
		Jun. 30, 2016	Dec. 31, 2015
Investment [Line Items]
Other investments, at fair value		$ 359,526	$ 336,856
Managed investments
Investment [Line Items]
Other investments, at fair value		359,526	336,856
Managed investments | Fund of hedge funds
Investment [Line Items]
Other investments, at fair value		959	1,417
Managed investments | Hedge funds
Investment [Line Items]
Other investments, at fair value		18,625	20,980
Managed investments | Private equity investments
Investment [Line Items]
Other investments, at fair value		73,306	63,771
Managed investments | Investment funds
Investment [Line Items]
Other investments, at fair value		203,871	188,721
Managed investments | Overseas deposits
Investment [Line Items]
Other investments, at fair value		55,301	54,484
Managed investments | Mutual funds
Investment [Line Items]
Other investments, at fair value		7,464	7,483
Recurring | Managed investments
Investment [Line Items]
Other investments, at fair value		359,526	336,856
Recurring | Managed investments | Fund of hedge funds
Investment [Line Items]
Other investments, at fair value		959	1,417
Recurring | Managed investments | Hedge funds
Investment [Line Items]
Other investments, at fair value		18,625	20,980
Recurring | Managed investments | Private equity investments
Investment [Line Items]
Other investments, at fair value		73,306	63,771
Recurring | Managed investments | Investment funds
Investment [Line Items]
Other investments, at fair value		203,871	188,721
Recurring | Managed investments | Overseas deposits
Investment [Line Items]
Other investments, at fair value		55,301	54,484
Recurring | Managed investments | Mutual funds
Investment [Line Items]
Other investments, at fair value		7,464	7,483
Subject to redemption restriction | Recurring | Managed investments
Investment [Line Items]
Other investments, at fair value		329,727	308,562
Subject to redemption restriction | Recurring | Managed investments | Fund of hedge funds
Investment [Line Items]
Other investments, at fair value		959	1,417
Subject to redemption restriction | Recurring | Managed investments | Hedge funds
Investment [Line Items]
Other investments, at fair value		18,625	20,980
Subject to redemption restriction | Recurring | Managed investments | Private equity investments
Investment [Line Items]
Other investments, at fair value		73,306	63,771
Subject to redemption restriction | Recurring | Managed investments | Investment funds
Investment [Line Items]
Other investments, at fair value		181,536	167,910
Subject to redemption restriction | Recurring | Managed investments | Overseas deposits
Investment [Line Items]
Other investments, at fair value		55,301	54,484
Subject to redemption restriction | Recurring | Managed investments | Mutual funds
Investment [Line Items]
Other investments, at fair value		0	0
Not subject to redemption restriction | Recurring | Managed investments
Investment [Line Items]
Other investments, at fair value		29,799	28,294
Not subject to redemption restriction | Recurring | Managed investments | Fund of hedge funds
Investment [Line Items]
Other investments, at fair value		0	0
Not subject to redemption restriction | Recurring | Managed investments | Hedge funds
Investment [Line Items]
Other investments, at fair value		0	0
Not subject to redemption restriction | Recurring | Managed investments | Private equity investments
Investment [Line Items]
Other investments, at fair value		$ 0	$ 0
Not subject to redemption restriction | Recurring | Managed investments | Investment funds
Investment [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	[1]	2 days	2 days
Other investments, at fair value		$ 22,335	$ 20,811
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Frequency	[1]	Daily	Daily
Not subject to redemption restriction | Recurring | Managed investments | Overseas deposits
Investment [Line Items]
Other investments, at fair value		$ 0	$ 0
Not subject to redemption restriction | Recurring | Managed investments | Mutual funds
Investment [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	[1]	1 day	1 day
Other investments, at fair value		$ 7,464	$ 7,483
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Frequency	[1]	Daily	Daily

[1] The redemption frequency and notice periods only apply to investments without redemption restrictions