Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]
Balance at Dec. 31, 2014	$ 2,021,456	$ 106,882	$ 1,754	$ 1,798,984	$ 176,120	$ (46,003)	$ (16,281)
Comprehensive income	132,133				120,527	11,606
Dividends declared:
Preferred stock	(6,030)				(6,030)
Common stock: $0.36/share	(63,330)				(63,330)
Issuance of common stock	7,229		12	3,651			3,566
Restricted stock compensation	3,286			3,286
Tax benefit of stock-based compensation	5			5
Balance at Sep. 30, 2015	2,094,749	106,882	1,766	1,805,926	227,287	(34,397)	(12,715)
Balance at Dec. 31, 2015	2,096,182	106,882	1,766	1,808,210	243,217	(51,133)	(12,760)
Comprehensive income	142,880				119,600	23,280
Dividends declared:
Preferred stock	(6,030)				(6,030)
Common stock: $0.36/share	(76,133)				(76,133)
Issuance of common stock	4,714		10	6,694			(1,990)
Issuance of common stock-acquisitions	404,031		341	403,690
Restricted stock compensation	4,644			4,644
Tax benefit of stock-based compensation	292			292
Balance at Sep. 30, 2016	$ 2,570,580	$ 106,882	$ 2,117	$ 2,223,530	$ 280,654	$ (27,853)	$ (14,750)