Allowance for Credit Losses and Credit Quality - Schedule of Allowance for Loan Losses for Covered Loan and Non-Covered Loan Portfolios (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses at beginning of period			$ 138,378	$ 130,131
Provision for (Reversal of) loan losses before benefit attributable to FDIC loss share agreements			25,974	13,292
Adjustment attributable to FDIC loss share arrangements			797	843
Net provision for loan losses	$ 11,866	$ 8,790	26,771	14,135
Adjustment attributable to FDIC loss share arrangements			(797)	(843)
Transfer of balance to OREO and other			967	9,765
Loans charged-off			(18,555)	(7,779)
Recoveries			2,622	2,270
Allowance for loan losses at end of period	147,452	128,149	147,452	128,149
Financing Receivable, Allowance For Credit Losses, Unfunded Commitments [Roll Forward]
Reserve for unfunded commitments at beginning of period			14,145	11,801
Provision for (Reversal of) unfunded lending commitments			(319)	1,443
Reserve for unfunded commitments at end of period	13,826	13,244	13,826	13,244
Allowance for credit losses at end of period	161,278	141,393	161,278	141,393
Legacy Loans
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses at beginning of period			93,808	76,174
Provision for (Reversal of) loan losses before benefit attributable to FDIC loss share agreements			28,390	12,631
Adjustment attributable to FDIC loss share arrangements			0	0
Net provision for loan losses			28,390	12,631
Adjustment attributable to FDIC loss share arrangements			0	0
Transfer of balance to OREO and other			0	0
Loans charged-off			(17,359)	(7,114)
Recoveries			2,022	2,032
Allowance for loan losses at end of period	106,861	83,723	106,861	83,723
Financing Receivable, Allowance For Credit Losses, Unfunded Commitments [Roll Forward]
Reserve for unfunded commitments at beginning of period			14,145	11,801
Provision for (Reversal of) unfunded lending commitments			(319)	1,443
Reserve for unfunded commitments at end of period	13,826	13,244	13,826	13,244
Allowance for credit losses at end of period	120,687	96,967	120,687	96,967
Acquired Loans
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for loan losses at beginning of period			44,570	53,957
Provision for (Reversal of) loan losses before benefit attributable to FDIC loss share agreements			(2,416)	661
Adjustment attributable to FDIC loss share arrangements			797	843
Net provision for loan losses			(1,619)	1,504
Adjustment attributable to FDIC loss share arrangements			(797)	(843)
Transfer of balance to OREO and other			967	9,765
Loans charged-off			(1,196)	(665)
Recoveries			600	238
Allowance for loan losses at end of period	40,591	44,426	40,591	44,426
Financing Receivable, Allowance For Credit Losses, Unfunded Commitments [Roll Forward]
Reserve for unfunded commitments at beginning of period			0	0
Provision for (Reversal of) unfunded lending commitments			0	0
Reserve for unfunded commitments at end of period	0	0	0	0
Allowance for credit losses at end of period	$ 40,591	$ 44,426	$ 40,591	$ 44,426