CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (USD $) In Thousands	Total	6.00% Series B Cumulative Convertible Preferred Stock	7.625% Series C Cumulative Redeemable Preferred Stock	7.50% Series D Cumulative Redeemable Preferred Stock	7.875% Series A Cumulative Redeemable Preferred Stock	Series D Preferred Stock	Common Stock Par Value	Common Stock Par Value 6.00% Series B Cumulative Convertible Preferred Stock	Additional Paid-In Capital	Additional Paid-In Capital 6.00% Series B Cumulative Convertible Preferred Stock	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Accumulated Deficit 6.00% Series B Cumulative Convertible Preferred Stock	Accumulated Deficit 7.625% Series C Cumulative Redeemable Preferred Stock	Accumulated Deficit 7.50% Series D Cumulative Redeemable Preferred Stock	Accumulated Deficit 7.875% Series A Cumulative Redeemable Preferred Stock	Accumulated Deficit Series D Preferred Stock	Total stockholders' equity	Total stockholders' equity 6.00% Series B Cumulative Convertible Preferred Stock	Total stockholders' equity 7.625% Series C Cumulative Redeemable Preferred Stock	Total stockholders' equity 7.50% Series D Cumulative Redeemable Preferred Stock	Total stockholders' equity 7.875% Series A Cumulative Redeemable Preferred Stock	Total stockholders' equity Series D Preferred Stock	Noncontrolling Interest	7.875% Series A Cumulative Redeemable Preferred Stock	7.625% Series C Cumulative Redeemable Preferred Stock	7.625% Series C Cumulative Redeemable Preferred Stock	7.50% Series D Cumulative Redeemable Preferred Stock	7.50% Series D Cumulative Redeemable Preferred Stock
Beginning balance at Dec. 31, 2011	$ 15,760,642						$ 9,702		$ 15,068,870		$ 3,008,988	$ (2,504,006)						$ 15,760,642							$ 177,088
Net income (loss)	1,735,900											1,735,900						1,735,900
Unrealized gains (losses) on available-for-sale securities	482,765										482,765							482,765
Reclassification adjustment for net (gains) losses included in net income (loss)	(438,511)										(438,511)							(438,511)
Exercise of stock options	8,438						6		8,432									8,438
Stock compensation expense	5,584								5,584									5,584
Conversion of Series B cumulative preferred stock	32,272	32,272						40		32,232									32,272
Net proceeds from direct purchase and dividend reinvestment	2,794						2		2,792									2,794
Contingent beneficial conversion feature on 4% Convertible Senior Notes	61,725								61,725									61,725
Equity component on 5% Convertible Senior Notes	11,717								11,717									11,717
Offering expenses	(248)								(248)									(248)
Preferred dividends declared		(289)	(14,297)	(10,351)	(14,593)								(289)	(14,297)	(10,351)	(14,593)			(289)	(14,297)	(10,351)	(14,593)
Net proceeds from Cumulative Redeemable Preferred Stock offering			290,514	445,457																290,514	445,457						290,514		445,457
Extinguishment of convertible debt	(53,558)								(53,558)									(53,558)
Buyback of common stock	(397,050)						(278)		(396,772)									(397,050)
Disposal of subsidiary	5,223											5,223						5,223
Common dividends declared, $1.20 per share	(1,989,690)											(1,989,690)						(1,989,690)
Ending balance at Dec. 31, 2012	15,924,444						9,472		14,740,774		3,053,242	(2,792,103)						15,924,444							177,088	290,514		445,457
Net income (loss)	3,729,698											3,729,698						3,729,698
Unrealized gains (losses) on available-for-sale securities	(5,378,089)										(5,378,089)							(5,378,089)
Reclassification adjustment for net (gains) losses included in net income (loss)	(424,086)										(424,086)							(424,086)
Exercise of stock options	2,204						2		2,202									2,204
Stock compensation expense	2,547						(2)		2,549									2,547
Net proceeds from direct purchase and dividend reinvestment	2,855						2		2,853									2,855
Contingent beneficial conversion feature on 4% Convertible Senior Notes	17,383								17,383									17,383
Preferred dividends declared			(22,875)		(14,593)	(34,500)								(22,875)		(14,593)	(34,500)			(22,875)		(14,593)	(34,500)
Disposal of subsidiary	20,923											20,923						20,923
Common dividends declared, $1.20 per share	(1,420,856)											(1,420,856)						(1,420,856)
Ending balance at Dec. 31, 2013	12,405,055						9,474		14,765,761		(2,748,933)	(534,306)						12,405,055							177,088	290,514		445,457
Net income (loss)	(842,083)											(842,083)						(842,083)
Net income (loss) attributable to noncontrolling interest	(196)																							(196)
Unrealized gains (losses) on available-for-sale securities	3,048,291										3,048,291							3,048,291
Reclassification adjustment for net (gains) losses included in net income (loss)	(94,475)										(94,475)							(94,475)
Stock compensation expense	1,072								1,072									1,072
Net proceeds from direct purchase and dividend reinvestment	2,370						2		2,368									2,370
Contingent beneficial conversion feature on 4% Convertible Senior Notes	17,308								17,308									17,308
Contributions from noncontrolling interest	5,486																							5,486
Preferred dividends declared			(22,875)		(14,593)	(34,500)								(22,875)		(14,593)	(34,500)			(22,875)		(14,593)	(34,500)
Common dividends declared, $1.20 per share	(1,137,079)											(1,137,079)						(1,137,079)
Ending balance at Dec. 31, 2014	$ 13,333,781						$ 9,476		$ 14,786,509		$ 204,883	$ (2,585,436)						$ 13,328,491						$ 5,290	$ 177,088	$ 290,514		$ 445,457