Parent Company Financial Statements - Statements of Cash Flows of Parent Company Only (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplemental Cash Flow Information [Line Items]
Net Income	$ 170,891	$ 159,649	$ 144,050
Other, net	10,702	(11,333)	(34,746)
Net cash flows provided by operating activities	292,708	223,480	446,819
Proceeds from sale of securities available for sale	615,199	33,499	175,872
Net cash received in business combinations	245,762	144,629	59,980
Net cash flows used in investing activities	(1,259,646)	(1,142,666)	(1,738,256)
Decrease in long-term debt	(173,477)	(34,968)	(96,906)
Increase in long-term debt	46,357	134,953	385,656
Net proceeds from issuance of common stock	18,472	12,731	12,857
Tax benefit of stock-based compensation	1,813	28	2,714
Preferred stock	(8,041)	(8,041)	(8,352)
Common stock	(101,670)	(84,511)	(81,220)
Net cash flows provided by financing activities	849,226	1,120,912	1,364,849
Net (Decrease) Increase in Cash and Cash Equivalents	(117,712)	201,726	73,412
Cash and cash equivalents at beginning of year	489,119	287,393	213,981
Cash and Cash Equivalents at End of Year	371,407	489,119	287,393
Interest	67,296	47,805	43,057
Parent Company [Member]
Supplemental Cash Flow Information [Line Items]
Net Income	170,891	159,649	144,050
Undistributed earnings from subsidiaries	(63,206)	(71,739)	(55,631)
Other, net	(2,530)	680	(637)
Net cash flows provided by operating activities	105,155	88,590	87,782
Proceeds from sale of securities available for sale	815		934
Net (increase) decrease in advances to subsidiaries	(6,263)	3,285	2,018
Payment for further investment in subsidiaries	(71,050)	(9,060)	(2,877)
Net cash received in business combinations	1,089		5,594
Net cash flows used in investing activities	(75,409)	(5,775)	5,669
Net decrease in advance from affiliate	6,356	(2,797)	(1,908)
Net decrease in short-term borrowings	(44)	(135)	(88)
Decrease in long-term debt	(10,291)	(650)	(34,865)
Increase in long-term debt	381	98,794	821
Net proceeds from issuance of common stock	18,472	12,731	12,857
Tax benefit of stock-based compensation	1,813	28	2,714
Preferred stock	(8,041)	(8,041)	(8,352)
Common stock	(101,670)	(84,511)	(81,220)
Net cash flows provided by financing activities	(93,024)	15,419	(110,041)
Net (Decrease) Increase in Cash and Cash Equivalents	(63,278)	98,234	(16,590)
Cash and cash equivalents at beginning of year	227,554	129,320	145,910
Cash and Cash Equivalents at End of Year	164,276	227,554	129,320
Interest	$ 13,620	$ 8,309	$ 9,112