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		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 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			38,015	17,855
Adjustment attributable to FDIC loss share arrangements			1,240	1,342
Net provision for loan losses	$ 12,484	$ 5,062	39,255	19,197
Adjustment attributable to FDIC loss share arrangements			(1,240)	(1,342)
Transfer of balance to OREO and other			2,045	9,768
Loans charged-off			(30,054)	(13,025)
Recoveries			3,899	5,061
Allowance for loan losses at end of period	148,193	130,254	148,193	130,254
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			(2,155)	2,724
Reserve for unfunded commitments at end of period	11,990	14,525	11,990	14,525
Allowance for credit losses at end of period	160,183	144,779	160,183	144,779
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			40,516	17,743
Adjustment attributable to FDIC loss share arrangements			0	0
Net provision for loan losses			40,516	17,743
Adjustment attributable to FDIC loss share arrangements			0	0
Transfer of balance to OREO and other			0	0
Loans charged-off			(28,559)	(12,073)
Recoveries			3,124	4,556
Allowance for loan losses at end of period	108,889	86,400	108,889	86,400
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			(2,155)	2,724
Reserve for unfunded commitments at end of period	11,990	14,525	11,990	14,525
Allowance for credit losses at end of period	120,879	100,925	120,879	100,925
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			(2,501)	112
Adjustment attributable to FDIC loss share arrangements			1,240	1,342
Net provision for loan losses			(1,261)	1,454
Adjustment attributable to FDIC loss share arrangements			(1,240)	(1,342)
Transfer of balance to OREO and other			2,045	9,768
Loans charged-off			(1,495)	(952)
Recoveries			775	505
Allowance for loan losses at end of period	39,304	43,854	39,304	43,854
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	$ 39,304	$ 43,854	$ 39,304	$ 43,854