Consolidated Condensed Statements Of Changes In Stockholders' Equity - USD ($) $ in Thousands	Total	Preferred Stock [Member]	Common Stock [Member]	Retained Earnings [Member]	Treasury Stock At Cost [Member]	Accumulated Other Comprehensive Income (loss) [Member]
Balance at Dec. 31, 2016		$ 0	$ 305,826	$ 535,631	$ (81,472)	$ (17,745)
Net Income	$ 61,411			61,411
Other comprehensive income, net of tax:
Unrealized net holding (loss) gain on securities available-for-sale, net of income taxes	4,740					4,740
Dividends on common shares at $3.11 per share				(43,411)
Cash payment for fractional shares in dividend reinvestment plan			(4)
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures			(795)	(197)	(645)
Allocated Share-based Compensation Expense	2,100		2,116
Treasury Stock, Value, Acquired, Cost Method					7,378
Balance at Sep. 30, 2017		0	307,143	553,434	(88,205)	(13,005)
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets				3,806		(3,806)
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets | Accounting Standards Update 2016-01 [Member]				1,917		(995)
Balance at Dec. 31, 2017	756,101	0	307,726	561,908	(87,079)	(26,454)
Balance (Adjustments for New Accounting Pronouncement [Member]) at Dec. 31, 2017				563,825		(27,449)
Net Income	84,126			84,126
Other comprehensive income, net of tax:
Unrealized net holding (loss) gain on securities available-for-sale, net of income taxes	(30,919)					(28,895)
Dividends on common shares at $3.11 per share				(48,349)
Cash payment for fractional shares in dividend reinvestment plan			(3)
Stock Issued During Period, Value, Acquisitions			48,519
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures			(1,597)	(317)	(1,304)
Allocated Share-based Compensation Expense	3,100		3,064
Treasury Stock, Value, Acquired, Cost Method					5,784
Balance at Sep. 30, 2018	$ 809,091	$ 0	$ 357,709	$ 603,091	$ (91,559)	$ (60,150)