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	51,366				40,343	11,023
Dividends declared:
Preferred stock	(2,010)				(2,010)
Common stock: $0.12/share	(20,992)				(20,992)
Issuance of common stock	4,435		9	5,986			(1,560)
Restricted stock compensation	340			340
Tax benefit of stock-based compensation	681			681
Balance at Mar. 31, 2015	2,055,276	106,882	1,763	1,805,991	193,461	(34,980)	(17,841)
Balance at Dec. 31, 2015	2,096,182	106,882	1,766	1,808,210	243,217	(51,133)	(12,760)
Comprehensive income	43,614				26,132	17,482
Dividends declared:
Preferred stock	(2,010)				(2,010)
Common stock: $0.12/share	(25,294)				(25,294)
Issuance of common stock	96		5	1,657			(1,566)
Issuance of common stock-acquisitions	404,020		341	403,679
Restricted stock compensation	1,136			1,136
Tax benefit of stock-based compensation	277			277
Balance at Mar. 31, 2016	$ 2,518,021	$ 106,882	$ 2,112	$ 2,214,959	$ 242,045	$ (33,651)	$ (14,326)