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]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance				$ 484,484
Cumulative Effect of New Accounting Principle in Period of Adoption				(2,057)
Balance at Dec. 31, 2014		$ 0	$ 303,104	486,541	$ (77,439)	$ (13,608)
Net Income	$ 60,123			60,123
Other comprehensive income, net of tax:
Unrealized net holding (loss) gain on securities available-for-sale, net of income taxes	6,179					6,179
Dividends on common shares at $2.82 per share				(43,462)
Cash payment for fractional shares in dividend reinvestment plan			(3)
Allocated Share-based Compensation Expense	704		704
Treasury Stock, Value, Acquired, Cost Method					(4,279)
Balance at Sep. 30, 2015		0	303,805	501,145	(81,718)	(7,429)
Balance at Dec. 31, 2015	713,355	0	303,966	507,505	(82,473)	(15,643)
Net Income	66,133			66,133
Other comprehensive income, net of tax:
Unrealized net holding (loss) gain on securities available-for-sale, net of income taxes	13,850					13,850
Dividends on common shares at $2.82 per share				(43,461)
Cash payment for fractional shares in dividend reinvestment plan			(3)
Allocated Share-based Compensation Expense	1,190		1,189
Balance at Sep. 30, 2016	$ 751,063	$ 0	$ 305,152	$ 530,177	$ (82,473)	$ (1,793)