Parent Company Information - Schedule of Condensed Statements of Cash Flows (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Net income	$ 131,961	$ 143,627	$ 132,511
Depreciation and amortization	19,712	18,477	16,380
Stock-based compensation	6,055	4,816	3,156
Net amortization of premiums and accretion of discounts on securities	16,229	21,124	11,871
Gains on securities transactions, net	(14,678)	(2,587)	(32,068)
Fair value of borrowings carried at fair value	(881)	(2,574)	(1,256)
Other assets	17,587	(49,345)	34,977
Net cash provided by operating activities	285,364	323,311	191,337
Sales	57,003	257,497	552,486
Maturities, calls and principal repayments	183,006	248,721	280,046
Cash and cash equivalents acquired in acquisitions		117,587
Net cash provided by (used in) investing activities	(786,026)	183,708	(192,841)
Issuance of long-term borrowings	125,000
Dividends paid to common shareholders	129,271	125,870	116,779
Common stock issued, net	7,071	7,805	8,027
Net cash used in financing activities	16,730	(32,968)	14,267
Net change in cash and cash equivalents	(483,932)	474,051	12,763
Cash and cash equivalents at beginning of year	853,100	379,049	366,286
Cash and cash equivalents at end of year	369,168	853,100	379,049
Parent Company [Member]
Net income	131,961	143,627	132,511
Equity in undistributed earnings of subsidiary	(21,494)	(7,381)	(27,131)
Depreciation and amortization	27	30	30
Stock-based compensation	6,055	4,816	3,156
Net amortization of premiums and accretion of discounts on securities	162	162	(56)
Gains on securities transactions, net	(14)
Fair value of borrowings carried at fair value	(881)	(2,574)	(1,256)
Other assets	(4,210)	2,977	535
Accrued expenses and other liabilities	1,124	(1,387)	132
Net cash provided by operating activities	112,730	140,270	107,921
Loan originations			(36,990)
Sales	643
Maturities, calls and principal repayments		1,000
Cash and cash equivalents acquired in acquisitions		3,934
Net cash provided by (used in) investing activities	643	4,934	(36,990)
Issuance of long-term borrowings	125,000
Redemption of junior subordinated debentures	(142,313)	(10,000)
Dividends paid to common shareholders	(129,271)	(125,870)	(116,779)
Common stock issued, net	7,071	7,805	8,027
Net cash used in financing activities	(139,513)	(128,065)	(108,752)
Net change in cash and cash equivalents	(26,140)	17,139	(37,821)
Cash and cash equivalents at beginning of year	59,867	42,728	80,549
Cash and cash equivalents at end of year	$ 33,727	$ 59,867	$ 42,728