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]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	$ (1,924)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance		$ 0	$ 302,651	$ 458,719	$ (76,128)	$ (35,419)
Balance at Dec. 31, 2013		0	302,651	460,643	(76,128)	(35,419)
Net Income	59,656			59,656
Other comprehensive income, net of tax:
Unrealized net holding (loss) gain on securities available-for-sale, net of income taxes	21,115					21,115
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	355		355
Treasury Stock, Value, Acquired, Cost Method					(1,485)
Balance at Sep. 30, 2014		0	303,003	474,913	(77,613)	(14,304)
Balance at Dec. 31, 2013		0	302,651	460,643	(76,128)	(35,419)
Balance at Dec. 31, 2014	696,541	0	303,104	486,541	(77,439)	(13,608)
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	(2,057)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance		0	303,104	484,484	(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	$ 715,803	$ 0	$ 303,805	$ 501,145	$ (81,718)	$ (7,429)