Consolidated Statement of Changes in Shareholders' Equity (Unaudited) - 9 months ended Sep. 30, 2016 - USD ($) $ in Thousands	Total	Common Stock [Member]	Surplus [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]
Balance at January 1, 2016 at Dec. 31, 2015	$ 1,712,635	$ 174,067	$ 752,997	$ 824,603	$ (38,212)	$ (820)
Beginning Balance, shares at Dec. 31, 2015		69,626,932
Comprehensive income:
Net income	107,977	$ 0	0	107,977	0	0
Other comprehensive income, net of tax	10,183	0	0	0	10,183	0
Total comprehensive income, net of tax	118,160
Stock based compensation expense	2,050	0	2,050	0	0	0
Acquisition of Bank of Georgetown (6,527,746)	264,495	$ 16,319	248,176	0	0	0
Acquisition of Bank of Georgetown, shares		6,527,746
Purchase of treasury stock	(1)	$ 0	0	0	0	(1)
Issuance of treasury stock	52	0	0	0	0	52
Distribution of treasury stock from deferred compensation plan	1	0	0	0	0	1
Cash dividends	(73,381)	0	0	(73,381)	0	0
Grant of restricted stock	0	$ 161	(161)	0	0	0
Grant of restricted stock, shares		64,092
Forfeiture of restricted stock	0	$ 0	207	0	0	(207)
Common stock options exercised	$ 4,668	$ 622	4,046	0	0	0
Common stock options exercised, shares	248,677	248,677
Balance at September 30, 2016 at Sep. 30, 2016	$ 2,028,679	$ 191,169	$ 1,007,315	$ 859,199	$ (28,029)	$ (975)
Ending Balance, shares at Sep. 30, 2016		76,467,447