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, 2013	$ 1,774,383	$ 106,882	$ 1,592	$ 1,608,117	$ 121,870	$ (56,924)	$ (7,154)
Comprehensive income	89,720				69,355	20,365
Dividends declared:
Preferred stock	(4,332)				(4,332)
Common stock: $0.24/share	(40,123)				(40,123)
Issuance of common stock	4,116		14	7,857	(228)		(3,527)
Issuance of common stock - acquisitions	81,389		67	81,322
Restricted stock compensation	1,419			1,419
Tax benefit of stock-based compensation	1,505			1,505
Balance at Jun. 30, 2014	1,908,077	106,882	1,673	1,700,220	146,542	(36,559)	(10,681)
Balance at Dec. 31, 2014	2,021,456	106,882	1,754	1,798,984	176,120	(46,003)	(16,281)
Comprehensive income	82,524				80,474	2,050
Dividends declared:
Preferred stock	(4,020)				(4,020)
Common stock: $0.24/share	(42,152)				(42,152)
Issuance of common stock	6,207		11	2,607			3,589
Restricted stock compensation	1,564			1,564
Tax benefit of stock-based compensation	192			192
Balance at Jun. 30, 2015	$ 2,065,771	$ 106,882	$ 1,765	$ 1,803,347	$ 210,422	$ (43,953)	$ (12,692)