Consolidated Statement of Shareholders' Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]
Stockholders' Equity Attributable to Parent at Dec. 31, 2014	$ 3,506,230	$ 1,042	$ (42,647)	$ 26,380	$ 3,807,167	$ (285,712)
Common Shares [Abstract]
Shares, Outstanding		103,044,257
Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures		20,940
Stock Issued During Period, Shares, Dividend Reinvestment Plan		1,300
Net earnings	73,079					73,079
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	2,364	0	0	2,364	0	0
Stock Granted, Value, Share-based Compensation, Net of Forfeitures	3,112	0	0	0	3,112	0
Stock Issued During Period, Value, Dividend Reinvestment Plan	58	0	0	0	58	0
Dividends, Common Stock, Cash	51,482	0	0	0	51,482	0
Stockholders' Equity Attributable to Parent at Mar. 31, 2015	$ 3,533,361	$ 1,042	$ (42,647)	$ 28,744	$ 3,758,855	$ (212,633)