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 (loss)	182,137				175,078	7,059
Dividends declared:
Preferred stock	(6,030)				(6,030)
Common stock: $0.36/share	(103,584)				(103,584)
Issuance of common stock	875		10	5,178			(4,313)
Issuance of common stock - acquisitions	1,783,424		1,116	1,782,308
Assumption of warrant due to acquisition	1,394			1,394
Restricted stock compensation	6,088			6,088
Balance at end of period at Sep. 30, 2017	4,435,921	106,882	3,251	4,029,334	369,861	(54,310)	(19,097)
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 (loss)	228,943				272,731	(43,788)
Dividends declared:
Preferred stock	(6,030)				(6,030)
Common stock: $0.36/share	(117,494)				(117,494)
Issuance of common stock	2,941		10	5,291			(2,360)
Restricted stock compensation	7,310			7,310
Balance at end of period at Sep. 30, 2018	$ 4,524,864	$ 106,882	$ 3,263	$ 4,046,168	$ 516,865	$ (126,840)	$ (21,474)