Condensed Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common stock	Preferred stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Non-controlling Interest
Common stock, shares outstanding, beginning balance at Dec. 31, 2018		112,940,595
Common stock, amount, beginning balance at Dec. 31, 2018		$ 1,129
Preferred stock, shares outstanding, beginning balance at Dec. 31, 2018			2,565,120
Preferred stock, amount, beginning balance at Dec. 31, 2018			$ 450,000
Total stockholders' equity, amount, beginning balance at Dec. 31, 2018	$ 2,200,871			$ 1,057,783	$ (52,130)	$ 764,056	$ (19,967)
Increase (Decrease) in Stockholders' Equity
Net income (loss)	85,339					91,758	(6,419)
Foreign currency translation adjustment, net of tax	(3,364)				(3,364)
Change in unrealized gain (loss) on investments, net of tax	60,755				56,075		4,680
Common stock dividends declared	(4,524)					(4,524)
Preferred stock dividends declared	(7,875)					(7,875)
Common stock issued under employee stock plans and exercises of stock options		292,276
Common stock issued under employee stock plans and exercises of stock options, value	93	$ 2		91
Shares withheld related to net share settlement, shares		(95,525)
Shares withheld related to net share settlement, value	(2,435)			(2,435)
Stock-based compensation	2,622			2,622
Common stock, shares outstanding, ending balance at Mar. 31, 2019		113,137,346
Common stock, amount, ending balance at Mar. 31, 2019		$ 1,131
Preferred stock, shares outstanding, ending balance at Mar. 31, 2019			2,565,120
Preferred stock, amount, ending balance at Mar. 31, 2019			$ 450,000
Total stockholders' equity, amount, ending balance at Mar. 31, 2019	$ 2,331,482			1,058,061	581	843,415	(21,706)
Common stock, shares outstanding, beginning balance at Dec. 31, 2019	113,368,811	113,368,811
Common stock, amount, beginning balance at Dec. 31, 2019		$ 1,134
Preferred stock, shares outstanding, beginning balance at Dec. 31, 2019	2,565,120		2,565,120
Preferred stock, amount, beginning balance at Dec. 31, 2019			$ 450,000
Total stockholders' equity, amount, beginning balance at Dec. 31, 2019	$ 2,617,494			1,065,634	74,548	1,058,138	(31,960)
Total stockholders' equity, amount, beginning balance (Accounting Standards Update 2016-13) at Dec. 31, 2019	(1,010)					(863)	(147)
Increase (Decrease) in Stockholders' Equity
Net income (loss)	100,573					100,759	(186)
Foreign currency translation adjustment, net of tax	(270)				(270)
Change in unrealized gain (loss) on investments, net of tax	(32,182)				(30,433)		(1,749)
Common stock dividends declared	(5,686)					(5,686)
Preferred stock dividends declared	(7,875)					(7,875)
Common stock issued under employee stock plans and exercises of stock options		487,414
Common stock issued under employee stock plans and exercises of stock options, value	388	$ 3		385
Shares withheld related to net share settlement, shares		(147,229)
Shares withheld related to net share settlement, value	(3,106)			(3,106)
Stock-based compensation	$ 3,162			3,162
Common stock, shares outstanding, ending balance at Mar. 31, 2020	113,708,996	113,708,996
Common stock, amount, ending balance at Mar. 31, 2020		$ 1,137
Preferred stock, shares outstanding, ending balance at Mar. 31, 2020	2,565,120		2,565,120
Preferred stock, amount, ending balance at Mar. 31, 2020			$ 450,000
Total stockholders' equity, amount, ending balance at Mar. 31, 2020	$ 2,671,488			$ 1,066,075	$ 43,845	$ 1,144,473	$ (34,042)