Significant Accounting Policies, Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Accumulated Other Comprehensive (Loss) Income [Roll Forward]
Beginning balance				$ 257,780
Ending balance		$ 245,414		245,414
Gain on investment in Regulus Therapeutics Inc.		20,211	$ 535	20,211	$ 535
Accumulated Other Comprehensive (Loss) Income [Member]
Accumulated Other Comprehensive (Loss) Income [Roll Forward]
Beginning balance		18,411	24,719	39,747	21,080
Ending balance		(17,957)	16,894	(17,957)	16,894
Unrealized Losses on Securities [Member]
Accumulated Other Comprehensive (Loss) Income [Roll Forward]
Other comprehensive losses before reclassifications, net of tax	[1]	(16,157)	(6,994)	(37,493)	(3,189)
Amounts reclassified from accumulated other comprehensive (loss) income	[2]	(20,211)	(831)	(20,211)	(997)
Net other comprehensive loss for the period		(36,368)	(7,825)	(57,704)	(4,186)
Income tax benefit included in other comprehensive income		$ 0	$ (2,500)	$ 0	$ 0

[1] Other comprehensive loss for the three months ended September 30, 2014 included income tax benefit of $2.5 million. There was no tax expense or benefit for the three and nine months ended September 30, 2015 and the nine months ended September 30, 2014.

[2] Amounts for the three and nine months ended September 30, 2015 are included in gain on investment in Regulus Therapeutics Inc. on our condensed consolidated statement of operations. For the three and nine months ended September 30, 2014, $0.5 million is included in the gain on investment in Regulus Therapeutics Inc., with the remaining amount included in gain on investments, net on our condensed consolidated statement of operations.