Condensed Financial Information - Parent Company - Condensed Statements of Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
CASH FLOWS FROM OPERATING ACTIVITIES:
NET EARNINGS	$ 104,774	$ 100,381	$ 89,559
Adjustments to reconcile net earnings to net cash provided by operating activities:
Depreciation and amortization, net	11,573	11,145	9,262
Decrease (increase) in other assets	2,397	(16,919)	9,852
Increase (decrease) in other liabilities	(2,643)	1,664	3,486
Net cash provided by operating activities	160,742	109,092	131,402
CASH FLOWS FROM INVESTING ACTIVITIES:
Net decrease in interest-bearing time deposits in unaffiliated banks	1,788	13,507	14,915
Purchases of bank premises and equipment	(20,399)	(17,433)	(17,412)
Net cash used in (provided by) investing activities	(251,960)	(384,225)	(575,205)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds of stock issuances	1,260	1,545	1,437
Cash dividends paid	(44,907)	(38,767)	(34,578)
Net cash provided by financing activities	74,818	294,548	485,262
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(16,400)	19,415	41,459
CASH AND CASH EQUIVALENTS, beginning of year	272,886	253,471	212,012
CASH AND CASH EQUIVALENTS, end of year	256,486	272,886	253,471
Parent Company [Member]
CASH FLOWS FROM OPERATING ACTIVITIES:
NET EARNINGS	104,774	100,381	89,559
Adjustments to reconcile net earnings to net cash provided by operating activities:
Excess of earnings over dividends of subsidiary bank	(58,809)	(52,911)	(58,539)
Depreciation and amortization, net	208	197	200
Decrease (increase) in other assets	1,702	507	(150)
Increase (decrease) in other liabilities	(1,374)	3,743	(314)
Other	8
Net cash provided by operating activities	46,509	51,917	30,756
CASH FLOWS FROM INVESTING ACTIVITIES:
Cash received (paid) in connection with acquisition of banks		13,125
Net decrease in interest-bearing time deposits in unaffiliated banks			480
Purchases of bank premises and equipment	(94)	(107)	(780)
Repayment from (of advances to) investment in and advances to subsidiaries, net		5,800	(3,300)
Other	10
Net cash used in (provided by) investing activities	(84)	18,818	(3,600)
CASH FLOWS FROM FINANCING ACTIVITIES:
Repayment of subordinated debt		(13,125)
Proceeds of stock issuances	1,260	1,545	1,437
Cash dividends paid	(44,907)	(38,767)	(34,578)
Net cash provided by financing activities	(43,647)	(50,347)	(33,141)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	2,778	20,388	(5,985)
CASH AND CASH EQUIVALENTS, beginning of year	90,473	70,085	76,070
CASH AND CASH EQUIVALENTS, end of year	$ 93,251	$ 90,473	$ 70,085