CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($)	Total	Series B Preferred Stock	Preferred Stock	Common Stock	Treasury Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income	Retained Earnings	Retained Earnings Series B Preferred Stock
Beginning Balance (in shares) at Dec. 31, 2017			4,000,000	432,376,250	11,087,337
Beginning Balance, shares issued (in shares) at Dec. 31, 2017				443,463,587
Beginning Balance at Dec. 31, 2017	$ 2,474,256,000		$ 400,000,000	$ 88,693,000	$ (107,644,000)	$ 1,222,277,000	$ 2,748,000	$ 868,182,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	126,254,000							126,254,000
Other comprehensive income, net of tax	12,261,000						12,261,000
Total comprehensive income	$ 138,515,000
Reclassification resulting from the adoption of ASU No. 2018-02							592,000	(592,000)
Cash dividends:
Cash dividends		$ (3,397,000)							$ (3,397,000)
Issuance of common shares (in shares)	5,559,991			5,559,991
Issuance of common shares	$ 16,699,000			$ 1,112,000		15,587,000
Stock-based compensation expense	$ 14,745,000					14,745,000
Common stock repurchased (in shares)	0
Shares repurchased related to employee stock-based compensation plans (in shares)	(2,740,018)			(2,740,018)	(2,740,018)
Shares repurchased related to employee stock-based compensation plans	$ (30,985,000)				$ (30,985,000)
Ending Balance (in shares) at Mar. 31, 2018			4,000,000	435,196,223	13,827,355
Ending Balance, shares issued (in shares) at Mar. 31, 2018				449,023,578
Ending Balance at Mar. 31, 2018	2,609,833,000		$ 400,000,000	$ 89,805,000	$ (138,629,000)	1,252,609,000	15,601,000	990,447,000
Beginning Balance (in shares) at Dec. 31, 2018			4,000,000	435,681,488	(14,174,733)
Beginning Balance, shares issued (in shares) at Dec. 31, 2018				449,856,221
Beginning Balance at Dec. 31, 2018	2,972,656,000		$ 400,000,000	$ 89,972,000	$ (142,591,000)	1,274,635,000	10,623,000	1,340,017,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	158,189,000							158,189,000
Other comprehensive income, net of tax	(8,446,000)						(8,446,000)
Total comprehensive income	149,743,000
Common stock dividend	$ (0.03)	(13,020,000)							(13,020,000)
Cash dividends:
Cash dividends		$ (4,468,000)							$ (4,468,000)
Issuance of common shares (in shares)	3,470,664			3,470,664
Issuance of common shares	$ 2,851,000			$ 694,000		2,157,000
Stock-based compensation expense	$ 13,891,000					13,891,000
Common stock repurchased (in shares)	5,435,476			5,435,476	(5,435,476)
Common stock retired	$ (60,000,000)				$ (60,000,000)
Shares repurchased related to employee stock-based compensation plans (in shares)	(1,289,391)			(1,289,391)	1,289,391
Shares repurchased related to employee stock-based compensation plans	$ (14,119,000)				$ (14,119,000)
Ending Balance (in shares) at Mar. 31, 2019			4,000,000	432,427,285	(20,899,600)
Ending Balance, shares issued (in shares) at Mar. 31, 2019				453,326,885
Ending Balance at Mar. 31, 2019	$ 3,047,534,000		$ 400,000,000	$ 90,666,000	$ (216,710,000)	$ 1,290,683,000	$ 2,177,000	$ 1,480,718,000