Investments - Schedule of reconciliation of the balances for all investments measured at fair value using significant unobservable inputs (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Assets
Asset fair value, beginning balance	$ 15,453	$ 13,760	$ 12,314	$ 3,857
Transfers in to (out of) Level 3	(3,552)	(7,915)	(1,631)	(1,047)
Purchases	3,205	5,421	4,710	7,075
Sales	(332)	(3,257)	(2,235)	(3,257)
Realized and Unrealized Gains (Losses)	921	865	2,537	2,246
Asset fair value, ending balance	15,695	8,874	15,695	8,874
Liabilities
Liability fair value, beginning balance		(4,012)		(2,510)
Transfers in to (out of) Level 3		0		0
Purchases		0		0
Sales		(2,710)		(4,805)
Realized and Unrealized Gains (Losses)		302		895
Liability fair value, ending balance		(6,420)		(6,420)
Derivative liabilities (free standing)
Liabilities
Liability fair value, beginning balance	(5,356)	(1,332)	(4,430)	0
Transfers in to (out of) Level 3	0	0	0	0
Purchases	0	0	0	0
Sales	0	(1,250)	(783)	(3,345)
Realized and Unrealized Gains (Losses)	(182)	342	(325)	1,105
Liability fair value, ending balance	(5,538)	(2,240)	(5,538)	(2,240)
Derivative liabilities (embedded)
Liabilities
Liability fair value, beginning balance		(2,680)		(2,510)
Transfers in to (out of) Level 3		0		0
Purchases		0		0
Sales		(1,460)		(1,460)
Realized and Unrealized Gains (Losses)		(40)		(210)
Liability fair value, ending balance		(4,180)		(4,180)
Asset-backed securities
Assets
Asset fair value, beginning balance	3,552	0	400	0
Transfers in to (out of) Level 3	(3,552)	309	(1,631)	309
Purchases	2,441	149	3,805	149
Sales	0	0	(1,903)	0
Realized and Unrealized Gains (Losses)	0	(264)	1,770	(264)
Asset fair value, ending balance	2,441	194	2,441	194
Bank debt
Assets
Asset fair value, beginning balance				54
Transfers in to (out of) Level 3				(54)
Purchases				0
Sales				0
Realized and Unrealized Gains (Losses)				0
Asset fair value, ending balance		0		0
Corporate bonds
Assets
Asset fair value, beginning balance	4,781	9,354	4,610	1,046
Transfers in to (out of) Level 3	0	(8,224)	0	(1,302)
Purchases	734	3,984	821	3,984
Sales	(332)	(1,120)	(332)	(1,120)
Realized and Unrealized Gains (Losses)	(30)	310	54	1,696
Asset fair value, ending balance	5,153	4,304	5,153	4,304
Private common equity securities
Assets
Asset fair value, beginning balance	2,012	4,406	2,012	2,757
Transfers in to (out of) Level 3	0	0	0	0
Purchases	0	0	0	1,654
Sales	0	(1,795)	0	(1,795)
Realized and Unrealized Gains (Losses)	288	862	288	857
Asset fair value, ending balance	2,300	3,473	2,300	3,473
Investments in limited partnerships
Assets
Asset fair value, beginning balance	5,108	0	5,292	0
Transfers in to (out of) Level 3	0	0	0	0
Purchases	0	1,288	54	1,288
Sales	0	(342)	0	(342)
Realized and Unrealized Gains (Losses)	663	(43)	425	(43)
Asset fair value, ending balance	5,771	903	5,771	903
Sovereign debt
Assets
Asset fair value, beginning balance	0		0
Transfers in to (out of) Level 3	0		0
Purchases	30		30
Sales	0		0
Realized and Unrealized Gains (Losses)	0		0
Asset fair value, ending balance	$ 30		$ 30

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Amount of gain (loss) recognized in the income statement for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of transfer of financial instrument classified as an asset into (out of) level 3 of the fair value hierarchy.

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Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of gain (loss) recognized on the income statement for financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of purchases of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of sales of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of transfers of financial instrument classified as a liability into (out of) level 3 of the fair value hierarchy.

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Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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