Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings
Stockholders' equity at beginning of period at Dec. 31, 2018	$ 2,399,101	$ 0	$ 90,369	$ 811,186	$ (52,432)	$ 1,549,978
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(11,420)					(11,420)
Other comprehensive income	1,102,416				1,102,416
Share-based compensation	7,360			7,360
Issuance of common stock under compensation plans	18		567	(549)
Stockholders' equity at end of period at Jun. 30, 2019	3,497,475	0	90,936	817,997	1,049,984	1,538,558
Stockholders' equity at beginning of period at Mar. 31, 2019	2,939,537	0	90,784	815,088	513,697	1,519,968
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	18,590					18,590
Other comprehensive income	536,287				536,287
Share-based compensation	3,155			3,155
Issuance of common stock under compensation plans	(94)		152	(246)
Stockholders' equity at end of period at Jun. 30, 2019	3,497,475	0	90,936	817,997	1,049,984	1,538,558
Stockholders' equity at beginning of period at Dec. 31, 2019	4,570,119	16	91,107	1,212,311	1,497,921	1,768,764
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(4,482)					(4,482)
Other comprehensive income	221,918				221,918
Issuance of preferred stock	290,260	12		290,248
Share-based compensation	4,394			4,394
Issuance of common stock under compensation plans	1,706		488	1,218
Cumulative effect of change in accounting principle	(9,295)					(9,295)
Dividends on preferred stock	(12,561)					(12,561)
Stockholders' equity at end of period at Jun. 30, 2020	5,062,059	28	91,595	1,508,171	1,719,839	1,742,426
Stockholders' equity at beginning of period at Mar. 31, 2020	3,522,757	16	91,498	1,215,464	219,974	1,995,805
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(247,429)					(247,429)
Other comprehensive income	1,499,865				1,499,865
Issuance of preferred stock	290,260	12		290,248
Share-based compensation	2,105			2,105
Issuance of common stock under compensation plans	451		97	354
Dividends on preferred stock	(5,950)					(5,950)
Stockholders' equity at end of period at Jun. 30, 2020	$ 5,062,059	$ 28	$ 91,595	$ 1,508,171	$ 1,719,839	$ 1,742,426