Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Preferred Equity	Common Stock	Surplus	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
Beginning balance at Dec. 31, 2015	$ 2,937,246	$ 121,379	$ 1,642	$ 1,458,522	$ 1,593,239	$ (32,616)	$ (204,920)
Comprehensive income:
Net income	42,534	0	0	0	42,534	0	0
Other comprehensive income	34,783	0	0	0	0	34,783	0
Comprehensive income	77,317
Common stock issued:
Stock-based compensation plans, net	2,205	0	0	613	(17,271)	0	18,863
Purchase of common stock returned to authorized but unissued	(20,007)	0	(12)	(19,995)	0	0	0
Purchase of treasury stock	(2,792)	0	0	0	0	0	(2,792)
Cash dividends:
Common stock dividends ($0.11 per share in 2016 and $0.12 per share in 2017)	(16,409)	0	0	0	(16,409)	0	0
Preferred stock dividends	(2,198)	0	0	0	(2,198)	0	0
Purchase of preferred stock	(1,092)	(1,032)	0	0	(60)	0	0
Stock-based compensation expense, net	8,066	0	0	8,066	0	0	0
Tax impact of stock-based compensation	162	0	0	162	0	0	0
Ending balance at Mar. 31, 2016	2,982,498	120,347	1,630	1,447,368	1,599,835	2,167	(188,849)
Beginning balance at Dec. 31, 2016	3,091,312	159,929	1,630	1,459,498	1,695,764	(54,679)	(170,830)
Comprehensive income:
Net income	56,270	0	0	0	56,270	0	0
Other comprehensive income	(1,665)	0	0	0	0	(1,665)	0
Comprehensive income	54,605
Common stock issued:
Stock-based compensation plans, net	17,940	0	0	868	(21,822)	0	38,894
Purchase of treasury stock	(7,743)	0	0	0	0	0	(7,743)
Cash dividends:
Common stock dividends ($0.11 per share in 2016 and $0.12 per share in 2017)	(18,368)	0	0	0	(18,368)	0	0
Preferred stock dividends	(2,330)	0	0	0	(2,330)	0	0
Stock-based compensation expense, net	8,344	0	0	8,344	0	0	0
Other	1,034	0	0	1,034	0	0	0
Ending balance at Mar. 31, 2017	$ 3,144,794	$ 159,929	$ 1,630	$ 1,469,744	$ 1,709,514	$ (56,344)	$ (139,679)