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	9 Months Ended	12 Months Ended
Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Dec. 31, 2012
Assets
Asset fair value, beginning balance	$ 8,874	$ 1,265	$ 3,857	$ 0
Transfers in to (out of) Level 3	(2,018)	95	(3,065)	411
Purchases	1,400	12	8,474	4,477
Sales	(192)	(325)	(3,448)	(4,098)
Realized and Unrealized Gains(Losses)	57	138	2,303	395
Asset fair value, ending balance	8,121	1,185	8,121	3,857
Derivative liabilities
Liabilities
Liability fair value, beginning balance	(2,240)		0
Transfers in to (out of) Level 3	0		0
Purchases	0		0
Sales	(990)		(4,335)
Realized and Unrealized Gains(Losses)	2,062		3,167
Liability fair value, ending balance	(1,168)		(1,168)
Asset-backed securities
Assets
Asset fair value, beginning balance	194		0
Transfers in to (out of) Level 3	(112)		196
Purchases	47		196
Sales	0		0
Realized and Unrealized Gains(Losses)	14		(249)
Asset fair value, ending balance	143		143
Bank debt
Assets
Asset fair value, beginning balance		0	54	0
Transfers in to (out of) Level 3		95	(54)	95
Purchases		12	0	3,384
Sales		0	0	(3,511)
Realized and Unrealized Gains(Losses)		8	0	147
Asset fair value, ending balance	0	115	0	54
Corporate bonds
Assets
Asset fair value, beginning balance	4,304	1,265	1,046	0
Transfers in to (out of) Level 3	0	0	(1,302)	316
Purchases	303	0	4,287	1,093
Sales	(192)	(325)	(1,311)	(587)
Realized and Unrealized Gains(Losses)	100	130	1,795	248
Asset fair value, ending balance	4,515	1,070	4,515	1,046
Private common equity securities
Assets
Asset fair value, beginning balance	3,473		2,757
Transfers in to (out of) Level 3	(1,906)		(1,905)
Purchases	379		2,032
Sales	0		(1,795)
Realized and Unrealized Gains(Losses)	(29)		828
Asset fair value, ending balance	1,917		1,917
Investment in limited partnership
Assets
Asset fair value, beginning balance	903		0
Transfers in to (out of) Level 3	0		0
Purchases	671		1,959
Sales	0		(342)
Realized and Unrealized Gains(Losses)	(28)		(71)
Asset fair value, ending balance	$ 1,546		$ 1,546

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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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