Loans, Leases and Allowance for Credit Losses - Loans by Risk Rating (Detail) - USD ($)	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	$ 11,112,854,000	$ 8,398,265,000
Current	11,046,589,000	8,366,782,000
Financing Receivable, Recorded Investment, Past Due	66,265,000	31,483,000
Residential real estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	322,939,000	299,402,000
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	26,905,000	33,009,000
Commercial real estate [Member] | Owner occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	2,083,285,000	1,732,888,000
Commercial real estate [Member] | Non-owner occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	2,104,577,000	1,869,941,000
Commercial real estate [Member] | Multi-family [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	178,959,000	182,625,000
Commercial and industrial [Member] | Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	5,114,257,000	3,326,708,000
Commercial and industrial [Member] | Leases [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	148,493,000	205,639,000
Construction and land development [Member] | Construction [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	694,527,000	388,399,000
Construction and land development [Member] | Land [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	438,912,000	359,654,000
Pass [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	10,805,542,000	8,143,813,000
Current	10,799,558,000	8,140,140,000
Pass [Member] | Residential real estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	310,067,000	284,052,000
Pass [Member] | Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	26,438,000	32,419,000
Pass [Member] | Commercial real estate [Member] | Owner occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	2,032,932,000	1,664,270,000
Pass [Member] | Commercial real estate [Member] | Non-owner occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	2,054,428,000	1,771,138,000
Pass [Member] | Commercial real estate [Member] | Multi-family [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	178,959,000	182,180,000
Pass [Member] | Commercial and industrial [Member] | Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	4,962,930,000	3,295,027,000
Pass [Member] | Commercial and industrial [Member] | Leases [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	140,531,000	202,772,000
Pass [Member] | Construction and land development [Member] | Construction [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	678,438,000	383,677,000
Pass [Member] | Construction and land development [Member] | Land [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	420,819,000	328,278,000
Watch [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	141,588,000	97,505,000
Current	140,932,000	95,091,000
Watch [Member] | Residential real estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	776,000	2,044,000
Watch [Member] | Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	209,000	233,000
Watch [Member] | Commercial real estate [Member] | Owner occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	28,422,000	28,072,000
Watch [Member] | Commercial real estate [Member] | Non-owner occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	14,867,000	35,752,000
Watch [Member] | Commercial real estate [Member] | Multi-family [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	0
Watch [Member] | Commercial and industrial [Member] | Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	76,283,000	14,380,000
Watch [Member] | Commercial and industrial [Member] | Leases [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	4,580,000	2,494,000
Watch [Member] | Construction and land development [Member] | Construction [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	16,089,000	4,241,000
Watch [Member] | Construction and land development [Member] | Land [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	362,000	10,289,000
Substandard [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	161,269,000	155,028,000
Current	104,232,000	129,787,000
Substandard [Member] | Residential real estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	12,096,000	13,306,000
Substandard [Member] | Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	258,000	357,000
Substandard [Member] | Commercial real estate [Member] | Owner occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	20,814,000	39,222,000
Substandard [Member] | Commercial real estate [Member] | Non-owner occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	35,282,000	62,611,000
Substandard [Member] | Commercial real estate [Member] | Multi-family [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	445,000
Substandard [Member] | Commercial and industrial [Member] | Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	74,294,000	17,146,000
Substandard [Member] | Commercial and industrial [Member] | Leases [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	794,000	373,000
Substandard [Member] | Construction and land development [Member] | Construction [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	481,000
Substandard [Member] | Construction and land development [Member] | Land [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	17,731,000	21,087,000
Doubtful [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	4,455,000	1,919,000
Current	1,867,000	1,764,000
Doubtful [Member] | Residential real estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	0
Doubtful [Member] | Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	0
Doubtful [Member] | Commercial real estate [Member] | Owner occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	1,117,000	1,324,000
Doubtful [Member] | Commercial real estate [Member] | Non-owner occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	440,000
Doubtful [Member] | Commercial real estate [Member] | Multi-family [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	0
Doubtful [Member] | Commercial and industrial [Member] | Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	750,000	155,000
Doubtful [Member] | Commercial and industrial [Member] | Leases [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	2,588,000	0
Doubtful [Member] | Construction and land development [Member] | Construction [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	0
Doubtful [Member] | Construction and land development [Member] | Land [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	0
Loss [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	0
Current	0	0
Loss [Member] | Residential real estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	0
Loss [Member] | Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	0
Loss [Member] | Commercial real estate [Member] | Owner occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	0
Loss [Member] | Commercial real estate [Member] | Non-owner occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	0
Loss [Member] | Commercial real estate [Member] | Multi-family [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	0
Loss [Member] | Commercial and industrial [Member] | Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	0
Loss [Member] | Commercial and industrial [Member] | Leases [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	0
Loss [Member] | Construction and land development [Member] | Construction [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	0
Loss [Member] | Construction and land development [Member] | Land [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	0
Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Recorded Investment, Past Due	30,184,000	7,842,000
Financing Receivables, 30 to 59 Days Past Due [Member] | Pass [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Recorded Investment, Past Due	1,907,000	2,771,000
Financing Receivables, 30 to 59 Days Past Due [Member] | Watch [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Recorded Investment, Past Due	271,000	198,000
Financing Receivables, 30 to 59 Days Past Due [Member] | Substandard [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Recorded Investment, Past Due	28,006,000	4,718,000
Financing Receivables, 30 to 59 Days Past Due [Member] | Doubtful [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	155,000
Financing Receivables, 30 to 59 Days Past Due [Member] | Loss [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Recorded Investment, Past Due	14,736,000	6,867,000
Financing Receivables, 60 to 89 Days Past Due [Member] | Pass [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Recorded Investment, Past Due	4,077,000	385,000
Financing Receivables, 60 to 89 Days Past Due [Member] | Watch [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Recorded Investment, Past Due	385,000	37,000
Financing Receivables, 60 to 89 Days Past Due [Member] | Substandard [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Recorded Investment, Past Due	10,274,000	6,445,000
Financing Receivables, 60 to 89 Days Past Due [Member] | Doubtful [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Financing Receivables, 60 to 89 Days Past Due [Member] | Loss [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	0
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Recorded Investment, Past Due	21,345,000	16,774,000
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Pass [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	517,000
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Watch [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Recorded Investment, Past Due	0	2,179,000
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Substandard [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Recorded Investment, Past Due	18,757,000	14,078,000
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Doubtful [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Recorded Investment, Past Due	2,588,000	0
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Loss [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Recorded Investment, Past Due	$ 0	$ 0