Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Preferred Stock	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
Balance at beginning of period at Dec. 31, 2014	$ 2,021,456	$ 106,882	$ 1,754	$ 1,798,984	$ 176,120	$ (46,003)	$ (16,281)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income	154,519				159,649	(5,130)
Dividends declared:
Preferred stock	(8,041)				(8,041)
Common stock: $0.48/share	(84,511)				(84,511)
Issuance of common stock	8,270		12	4,737			3,521
Restricted stock compensation	4,461			4,461
Tax benefit of stock-based compensation	28			28
Balance at end of period at Dec. 31, 2015	2,096,182	106,882	1,766	1,808,210	243,217	(51,133)	(12,760)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income	160,655				170,891	(10,236)
Dividends declared:
Preferred stock	(8,041)				(8,041)
Common stock: $0.48/share	(101,670)				(101,670)
Issuance of common stock	11,406		19	13,411			(2,024)
Issuance of common stock – acquisitions	404,206		340	403,866
Restricted stock compensation	7,066			7,066
Tax benefit of stock-based compensation	1,813			1,813
Balance at end 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	192,237				199,204	(6,967)
Dividends declared:
Preferred stock	(8,041)				(8,041)
Common stock: $0.48/share	(142,618)				(142,618)
Issuance of common stock	2,980		12	7,298			(4,330)
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	8,201			8,201
Reclassification due to tax reform					14,716	(14,716)
Balance at end of period at Dec. 31, 2017	$ 4,409,194	$ 106,882	$ 3,253	$ 4,033,567	$ 367,658	$ (83,052)	$ (19,114)