Condensed Parent Company Financial Statements (Detail) - Statements of Cash Flows (Parent Company Only) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Activities
Net income (loss)	$ 69,306	$ 79,306	$ (21,054)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation of premises, furniture, and equipment	12,224	11,038	10,874
Net securities (gains) losses	(8,097)	(34,164)	921
Net losses on early extinguishment of debt	2,059	1,034	558
Share-based compensation expense	5,926	5,903	6,004
Tax (expense) benefit related to share-based compensation	(106)	(10)	170
Net decrease (increase) in other assets	(10,651)	30,696	10,117
Net increase (decrease) in other liabilities	22,367	(21,859)	8,973
Net cash provided by operating activities	122,927	133,368	169,824
Investing Activities
Purchases of securities available-for-sale	(25,856)	(335,442)	(588,429)
Purchases of premises, furniture, and equipment	(14,085)	(11,030)	(8,764)
Cash received from acquisitions, net of cash paid	200,645	0	0
Net cash provided by (used in) investing activities	111,672	(369,296)	(144,607)
Financing Activities
Payments for retirement of subordinated debt	0	(24,094)	(37,033)
Treasury stock activity	(369)	(29)	(40)
Cash dividends paid	(22,568)	(7,508)	(2,977)
Restricted stock activity	(2,781)	(1,607)	(1,469)
Excess tax benefit (expense) related to share-based compensation	912	79	(21)
Net cash (used in) provided by financing activities	(215,578)	106,903	49,519
Net increase (decrease) in cash and cash equivalents	19,021	(129,025)	74,736
Cash and cash equivalents at beginning of year	587,241	716,266	641,530
Cash and cash equivalents at end of year	606,262	587,241	716,266
Common stock issued for acquisitions, net of issuance costs	38,300	0	0
Parent Company
Operating Activities
Net income (loss)	69,306	79,306	(21,054)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Equity in undistributed (income) loss of subsidiaries	(26,280)	(23,147)	40,355
Depreciation of premises, furniture, and equipment	6	7	6
Net securities (gains) losses	(5,702)	(34,119)	0
Net losses on early extinguishment of debt	0	1,034	558
Share-based compensation expense	5,926	5,903	6,004
Tax (expense) benefit related to share-based compensation	(106)	(10)	170
Net decrease (increase) in other assets	4,599	1,084	(6,207)
Net increase (decrease) in other liabilities	14,063	(1,624)	1,366
Net cash provided by operating activities	61,812	28,434	21,198
Investing Activities
Purchases of securities available-for-sale	0	(46,532)	(5,811)
Proceeds from sales and maturities of securities available-for-sale	8,540	43,329	0
Purchases of premises, furniture, and equipment	0	0	(18)
Cash received from acquisitions, net of cash paid	(15,809)	0	0
Net cash provided by (used in) investing activities	(7,269)	(3,203)	(5,829)
Financing Activities
Payments for retirement of subordinated debt	0	(24,094)	(37,033)
Treasury stock activity	369	0	0
Cash dividends paid	(22,568)	(7,508)	(2,977)
Restricted stock activity	(2,781)	(1,607)	(1,469)
Excess tax benefit (expense) related to share-based compensation	912	79	(21)
Net cash (used in) provided by financing activities	(24,068)	(33,130)	(41,500)
Net increase (decrease) in cash and cash equivalents	30,475	(7,899)	(26,131)
Cash and cash equivalents at beginning of year	13,071	20,970	47,101
Cash and cash equivalents at end of year	43,546	13,071	20,970
Common stock issued for acquisitions, net of issuance costs	$ 38,300	$ 0	$ 0