Organization and Significant Accounting Policies, Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		$ 257,780
Amounts reclassified from accumulated other comprehensive (loss) income		(20,211)	$ (21,412)	$ (1,653)
Ending balance		200,790	257,780
Income tax expense included in other comprehensive income		0	12,800	5,900
Gain on investment in Regulus Therapeutics Inc.		20,211	19,902	0
Accumulated Other Comprehensive (Loss) Income [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		39,747	21,080	12,480
Ending balance		(13,565)	39,747	21,080
Unrealized (Losses) Gains on Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Other comprehensive (loss) income before reclassifications, net of tax	[1]	(33,101)	40,079	10,253
Amounts reclassified from accumulated other comprehensive (loss) income	[2]	(20,211)	(21,412)	(1,653)
Net other comprehensive (loss) income for the period		$ (53,312)	$ 18,667	$ 8,600

[1] Other comprehensive income includes income tax expense of $12.8 million and $5.9 million for the years ended December 31, 2014 and 2013, respectively. There was no tax expense for other comprehensive income for the year ended December 31, 2015.

[2] Amounts for 2015 are included in the separate line called "Gain on investment in Regulus Therapeutics Inc." on our Consolidated Statement of Operations. For 2014, $19.9 million is included in a separate line called "Gain on investment in Regulus Therapeutics Inc.", with the remaining amount included in a separate line called "Gain on investments, net" on our Consolidated Statement of Operations. Amounts for 2013 are included in a separate line called "Gain on investments, net" on our Consolidated Statement of Operations.