Condensed Parent Company Financial Statements - Schedule of Condensed Cash Flow Statement (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
OPERATING ACTIVITIES
Net income	$ 24,218	$ 17,435	$ 22,109	$ 22,874	$ 23,002	$ 22,248	$ 21,633	$ 13,887	$ 86,635	$ 80,762	$ 69,974
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed net income									(900)	(600)	(900)
Gain on securities									(2,357)	(948)	(903)
Decrease in other assets									13,137	(4,293)	10,205
Other - net									1,448	1,914	5,328
Net cash provided by operating activities									123,697	88,649	94,808
INVESTING ACTIVITIES
Proceed from sales - securities available-for-sale									277,225	635,609	16,249
Acquisitions and additional capitalization of subsidiaries, net of cash (paid) acquired									4,863	(28,551)
Net cash provided (used in) by investing activities									193,968	(210,591)	(173,006)
FINANCING ACTIVITIES
Repayment of junior subordinated debt										(36,083)
Issuance of common stock									1,713
Repurchase of common stock warrant										(2,247)
Treasury shares (purchased) sold - net									(3,026)	(2,542)	1,918
Net cash (used in) provided by financing activities									(276,180)	114,625	76,649
Net increase (decrease) in cash and cash equivalents									41,485	(7,317)	(1,549)
Cash and cash equivalents at beginning of the year				86,685				94,002	86,685	94,002	95,551
Cash and cash equivalents at end of the year	128,170				86,685				128,170	86,685	94,002
Parent Company [Member]
OPERATING ACTIVITIES
Net income									86,635	80,762	69,974
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed net income									(7,228)	(25,974)	(13,118)
Gain on securities											(745)
Decrease in other assets									14,679	199	1,908
Other - net									2,094	1,657	1,968
Net cash provided by operating activities									96,180	56,644	59,987
INVESTING ACTIVITIES
Proceed from sales - securities available-for-sale										210	1,990
Acquisitions and additional capitalization of subsidiaries, net of cash (paid) acquired									(43,199)	1,465
Net cash provided (used in) by investing activities									(43,199)	1,675	1,990
FINANCING ACTIVITIES
Repayment of junior subordinated debt										(36,083)
Repayment of other borrowings										(13,000)
Issuance of common stock									1,713
Repurchase of common stock warrant										(2,247)
Treasury shares (purchased) sold - net									(3,026)	(2,542)	1,918
Dividends paid to common and preferred shareholders									(37,805)	(33,007)	(25,136)
Net cash (used in) provided by financing activities									(39,118)	(86,879)	(23,218)
Net increase (decrease) in cash and cash equivalents									13,863	(28,560)	38,759
Cash and cash equivalents at beginning of the year				$ 33,172				$ 61,732	33,172	61,732	22,973
Cash and cash equivalents at end of the year	$ 47,035				$ 33,172				$ 47,035	$ 33,172	$ 61,732