CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Preferred Stock	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comp. Income (Loss), net	Accounting Standards Update 2016-13	Accounting Standards Update 2016-13 Retained Earnings
Balance at Dec. 31, 2018	$ 3,965,940		$ 77,484	$ 3,107,431	$ 833,130	$ (52,105)
Balance (in shares) at Dec. 31, 2018			77,484,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of employee common stock options & related tax benefits	130		$ 5	125
Exercise of employee common stock options and related tax benefits (in shares)			5,000
Common dividends paid	(12,545)				(12,545)
Repurchase of common stock	(30,049)		$ (543)	(29,506)
Repurchase of common stock (in shares)			(543,000)
Issuance of restricted common shares, net of forfeitures	0		$ 180	(180)
Issuance of restricted common shares, net of forfeitures (in shares)			180,000
Restricted shares withheld for taxes & related benefits	(3,487)		$ (62)	(3,425)
Restricted shares withheld for taxes (in shares)			(62,000)
Stock-based compensation expense	4,913			4,913
Net income	93,960				93,960
Other comprehensive income (loss)	37,077					37,077
Balance at Mar. 31, 2019	4,055,939		$ 77,064	3,079,358	914,545	(15,028)
Balance (in shares) at Mar. 31, 2019			77,064,000
Balance at Dec. 31, 2018	3,965,940		$ 77,484	3,107,431	833,130	(52,105)
Balance (in shares) at Dec. 31, 2018			77,484,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	15,091
Net income	304,802
Other comprehensive income (loss)	99,247
Balance at Sep. 30, 2019	4,294,630		$ 76,736	3,070,235	1,100,517	47,142
Balance (in shares) at Sep. 30, 2019			76,736,000
Balance at Mar. 31, 2019	4,055,939		$ 77,064	3,079,358	914,545	(15,028)
Balance (in shares) at Mar. 31, 2019			77,064,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of employee common stock options & related tax benefits	9		$ 1	8
Exercise of employee common stock options and related tax benefits (in shares)			1,000
Common dividends paid	(12,432)				(12,432)
Repurchase of common stock	(7,375)		$ (132)	(7,243)
Repurchase of common stock (in shares)			(132,000)
Issuance of restricted common shares, net of forfeitures	0		$ 10	(10)
Issuance of restricted common shares, net of forfeitures (in shares)			10,000
Restricted shares withheld for taxes & related benefits	(801)		$ (14)	(787)
Restricted shares withheld for taxes (in shares)			(14,000)
Stock-based compensation expense	5,160			5,160
Net income	100,321				100,321
Other comprehensive income (loss)	35,540					35,540
Balance at Jun. 30, 2019	$ 4,176,361		$ 76,929	3,076,486	1,002,434	20,512
Balance (in shares) at Jun. 30, 2019			76,929,000
Common Stock, Dividends, Per Share, Cash Paid	$ 0.16
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of employee common stock options & related tax benefits	$ 108		$ 4	104
Exercise of employee common stock options and related tax benefits (in shares)			4,000
Common dividends paid	(12,438)				(12,438)
Repurchase of common stock	(11,065)		$ (198)	(10,867)
Repurchase of common stock (in shares)			(198,000)
Issuance of restricted common shares, net of forfeitures	0		$ 10	(10)
Issuance of restricted common shares, net of forfeitures (in shares)			10,000
Restricted shares withheld for taxes & related benefits	(505)		$ (9)	(496)
Restricted shares withheld for taxes (in shares)			(9,000)
Stock-based compensation expense	5,018			5,018
Net income	110,521				110,521
Other comprehensive income (loss)	26,630					26,630
Balance at Sep. 30, 2019	4,294,630		$ 76,736	3,070,235	1,100,517	47,142
Balance (in shares) at Sep. 30, 2019			76,736,000
Balance at Dec. 31, 2019	4,355,748		$ 76,564	3,064,467	1,184,183	30,534
Balance (in shares) at Dec. 31, 2019			76,564,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of employee common stock options & related tax benefits	5		$ 1	4
Exercise of employee common stock options and related tax benefits (in shares)			1,000
Common dividends paid	(12,442)				(12,442)
Repurchase of common stock	(50,790)		$ (1,015)	(49,775)
Repurchase of common stock (in shares)			(1,015,000)
Issuance of restricted common shares, net of forfeitures	0		$ 198	(198)
Issuance of restricted common shares, net of forfeitures (in shares)			198,000
Restricted shares withheld for taxes & related benefits	(1,957)		$ (32)	(1,925)
Restricted shares withheld for taxes (in shares)			(32,000)
Issuance of common stock pursuant to restricted stock unit agreement, net of shares withheld for taxes & related tax benefits	2,469		$ 84	(2,553)
Issuance of common stock pursuant to restricted stock unit agreement, net of shares withheld for taxes and related tax benefit (in shares)			84,000
Stock-based compensation expense	5,501			5,501
Net income	28,356				28,356
Cumulative effect of change in accounting principle							$ (31,796)	$ (31,796)
Other comprehensive income (loss)	94,972					94,972
Balance at Mar. 31, 2020	4,385,128		$ 75,800	3,015,521	1,168,301	125,506
Balance (in shares) at Mar. 31, 2020			75,800,000
Balance at Dec. 31, 2019	4,355,748		$ 76,564	3,064,467	1,184,183	30,534
Balance (in shares) at Dec. 31, 2019			76,564,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	14,092
Net income	201,445
Other comprehensive income (loss)	127,454
Balance at Sep. 30, 2020	4,787,308	$ 217,126	$ 75,835	3,023,430	1,312,929	157,988
Balance (in shares) at Sep. 30, 2020			75,835,000
Balance at Mar. 31, 2020	4,385,128		$ 75,800	3,015,521	1,168,301	125,506
Balance (in shares) at Mar. 31, 2020			75,800,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of preferred stock, net of issuance costs	217,632	217,632
Exercise of employee common stock options & related tax benefits	225		$ 9	216
Exercise of employee common stock options and related tax benefits (in shares)			9,000
Common dividends paid	(12,378)				(12,378)
Issuance of restricted common shares, net of forfeitures	0		$ 38	(38)
Issuance of restricted common shares, net of forfeitures (in shares)			38,000
Restricted shares withheld for taxes & related benefits	(553)		$ (13)	(540)
Restricted shares withheld for taxes (in shares)			(13,000)
Issuance of common stock pursuant to restricted stock unit agreement, net of shares withheld for taxes & related tax benefits	19		$ 2	(21)
Issuance of common stock pursuant to restricted stock unit agreement, net of shares withheld for taxes and related tax benefit (in shares)			2,000
Stock-based compensation expense	4,148			4,148
Net income	62,444				62,444
Other comprehensive income (loss)	39,020					39,020
Balance at Jun. 30, 2020	$ 4,695,647	217,632	$ 75,836	3,019,286	1,218,367	164,526
Balance (in shares) at Jun. 30, 2020			75,836,000
Common Stock, Dividends, Per Share, Cash Paid	$ 0.16
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of preferred stock, net of issuance costs	$ (506)	(506)
Preferred dividends paid	3,798				3,798
Common dividends paid	(12,285)				(12,285)
Issuance of restricted common shares, net of forfeitures	0		$ 6	(6)
Issuance of restricted common shares, net of forfeitures (in shares)			6,000
Restricted shares withheld for taxes & related benefits	(300)		$ (7)	(293)
Restricted shares withheld for taxes (in shares)			(7,000)
Stock-based compensation expense	4,443			4,443
Net income	110,645				110,645
Other comprehensive income (loss)	(6,538)					(6,538)
Balance at Sep. 30, 2020	$ 4,787,308	$ 217,126	$ 75,835	$ 3,023,430	$ 1,312,929	$ 157,988
Balance (in shares) at Sep. 30, 2020			75,835,000