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	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)
Balance at Dec. 31, 2015	2,096,182	106,882	1,766	1,808,210	243,217	(51,133)	(12,760)
Comprehensive income	93,106				67,432	25,674
Dividends declared:
Preferred stock	(4,020)				(4,020)
Common stock: $0.24/share	(50,708)				(50,708)
Issuance of common stock	3,687		9	5,284			(1,606)
Issuance of common stock - acquisitions	404,031		341	403,690
Restricted stock compensation	2,916			2,916
Tax benefit of stock-based compensation	143			143
Balance at Jun. 30, 2016	$ 2,545,337	$ 106,882	$ 2,116	$ 2,220,243	$ 255,921	$ (25,459)	$ (14,366)