Organization and Significant Accounting Policies, Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		$ 200,790
Net other comprehensive (loss) income for the period		(16,793)	$ (53,312)	$ 18,667
Ending balance		99,565	200,790
Income tax expense included in other comprehensive income		0	0	12,800
Gain on investment in Regulus Therapeutics Inc.		0	20,211	19,902
Accumulated Other Comprehensive (Loss) Income [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		(13,565)	39,747	21,080
Ending balance		(30,358)	(13,565)	39,747
Unrealized (Losses) Gains on Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Unrealized (losses) gains, net of tax	[1]	(17,219)	(33,101)	40,079
Amounts reclassified from accumulated other comprehensive (loss) income	[2]	447	(20,211)	(21,412)
Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Unrealized (losses) gains, net of tax		$ (21)	$ 0	$ 0

[1] Other comprehensive income includes income tax expense of $12.8 million for the year ended December 31, 2014. There was no tax expense for other comprehensive income for the years ended December 31, 2016 or 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.