Condensed Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Preferred stock	Common stock	Treasury Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Non-controlling Interest
Total stockholders' equity, amount, beginning balance at Dec. 31, 2018	$ 2,200,871	$ 450,000	$ 1,129		$ 1,057,783	$ (52,130)	$ 764,056	$ (19,967)
Increase (Decrease) in Stockholders' Equity
Net income (loss)	222,636						240,788	(18,152)
Foreign currency translation adjustment, net of tax	(6,440)					(6,440)
Change in unrealized gain (loss) on investments, net of tax	148,861					138,957		9,904
Common stock dividends declared	(14,714)						(14,714)
Preferred stock dividends declared	(24,675)						(24,675)
Common stock issued under employee stock plans and exercises of stock options, value	436		4		432
Shares withheld related to net share settlement, value	(3,633)				(3,633)
Stock-based compensation	8,277				8,277
Total stockholders' equity, amount, ending balance at Sep. 30, 2019	2,531,619	450,000	1,133		1,062,859	80,387	965,455	(28,215)
Total stockholders' equity, amount, beginning balance at Jun. 30, 2019	2,460,868	450,000	1,132		1,060,379	59,910	907,841	(18,394)
Increase (Decrease) in Stockholders' Equity
Net income (loss)	60,239						71,154	(10,915)
Foreign currency translation adjustment, net of tax	(3,242)					(3,242)
Change in unrealized gain (loss) on investments, net of tax	24,813					23,719		1,094
Common stock dividends declared	(5,665)						(5,665)
Preferred stock dividends declared	(7,875)						(7,875)
Common stock issued under employee stock plans and exercises of stock options, value	189		1		188
Shares withheld related to net share settlement, value	(493)				(493)
Stock-based compensation	2,785				2,785
Total stockholders' equity, amount, ending balance at Sep. 30, 2019	2,531,619	450,000	1,133		1,062,859	80,387	965,455	(28,215)
Increase (Decrease) in Stockholders' Equity
Cumulative Effect of New Accounting Principle in Period of Adoption	(1,010)
Cumulative Effect of New Accounting Principle in Period of Adoption | Accounting Standards Update 2016-13	(147)						(863)
Total stockholders' equity, amount, beginning balance at Dec. 31, 2019	2,617,494	450,000	1,134	$ 0	1,065,634	74,548	1,058,138	(31,960)
Increase (Decrease) in Stockholders' Equity
Net income (loss)	392,055						377,302	14,753
Foreign currency translation adjustment, net of tax	(436)					(436)
Change in unrealized gain (loss) on investments, net of tax	119,990					120,841		(851)
Common stock repurchased	(8,482)			(8,482)
Common stock dividends declared	(17,030)						(17,030)
Preferred stock dividends declared	(24,675)						(24,675)
Common stock issued under employee stock plans and exercises of stock options, value	1,970		5		1,965
Shares withheld related to net share settlement, value	(3,647)				(3,647)
Stock-based compensation	9,336				9,336
Total stockholders' equity, amount, ending balance at Sep. 30, 2020	3,085,565	450,000	1,139	(8,482)	1,073,288	194,953	1,392,872	(18,205)
Total stockholders' equity, amount, beginning balance at Jun. 30, 2020	2,979,676	450,000	1,139	(8,482)	1,069,152	186,864	1,296,451	(15,448)
Increase (Decrease) in Stockholders' Equity
Net income (loss)	116,869						109,969	6,900
Foreign currency translation adjustment, net of tax	48					48
Change in unrealized gain (loss) on investments, net of tax	(1,616)					8,041		(9,657)
Common stock repurchased				0
Common stock dividends declared	(5,673)						(5,673)
Preferred stock dividends declared	(7,875)						(7,875)
Common stock issued under employee stock plans and exercises of stock options, value	1,134		0		1,134
Shares withheld related to net share settlement, value	(156)				(156)
Stock-based compensation	3,158				3,158
Total stockholders' equity, amount, ending balance at Sep. 30, 2020	$ 3,085,565	$ 450,000	$ 1,139	$ (8,482)	$ 1,073,288	$ 194,953	$ 1,392,872	$ (18,205)