Consolidated Statements of Stockholders' Equity - 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 beginning of period at Dec. 31, 2016	$ 2,571,617	$ 106,882	$ 2,125	$ 2,234,366	$ 304,397	$ (61,369)	$ (14,784)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income	102,371				97,385	4,986
Dividends declared:
Preferred stock	(4,020)				(4,020)
Common stock: $0.24/share	(64,561)				(64,561)
Issuance of common stock	(256)		9	4,039			(4,304)
Issuance of common stock - acquisitions	1,781,935		1,116	1,780,819
Assumption of warrant due to acquisition	1,394			1,394
Restricted stock compensation	3,958			3,958
Balance at end of period at Jun. 30, 2017	4,392,438	106,882	3,250	4,024,576	333,201	(56,383)	(19,088)
Balance at beginning of period at Dec. 31, 2017	4,409,194	106,882	3,253	4,033,567	367,658	(83,052)	(19,114)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income	139,135				171,968	(32,833)
Dividends declared:
Preferred stock	(4,020)				(4,020)
Common stock: $0.24/share	(78,280)				(78,280)
Issuance of common stock	2,514		9	4,858			(2,353)
Restricted stock compensation	4,699			4,699
Balance at end of period at Jun. 30, 2018	$ 4,473,242	$ 106,882	$ 3,262	$ 4,043,124	$ 457,326	$ (115,885)	$ (21,467)