Loans Receivable, Net - Risk Category of Loans by Loan Portfolio Segment Excluding PCI Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loan	$ 3,089,172	$ 1,943,444
Commercial and Industrial
Financing Receivable, Recorded Investment [Line Items]
Loan	342,555	187,645
Commercial Real Estate - Owner Occupied
Financing Receivable, Recorded Investment [Line Items]
Loan	734,720	569,497
Commercial Real Estate - Investor
Financing Receivable, Recorded Investment [Line Items]
Loan	2,011,897	1,186,302
Pass
Financing Receivable, Recorded Investment [Line Items]
Loan	2,996,381	1,874,637
Pass | Commercial and Industrial
Financing Receivable, Recorded Investment [Line Items]
Loan	330,996	181,438
Pass | Commercial Real Estate - Owner Occupied
Financing Receivable, Recorded Investment [Line Items]
Loan	709,902	546,569
Pass | Commercial Real Estate - Investor
Financing Receivable, Recorded Investment [Line Items]
Loan	1,955,483	1,146,630
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loan	25,805	22,134
Special Mention | Commercial and Industrial
Financing Receivable, Recorded Investment [Line Items]
Loan	423	3,153
Special Mention | Commercial Real Estate - Owner Occupied
Financing Receivable, Recorded Investment [Line Items]
Loan	2,202	4,337
Special Mention | Commercial Real Estate - Investor
Financing Receivable, Recorded Investment [Line Items]
Loan	23,180	14,644
Substandard
Financing Receivable, Recorded Investment [Line Items]
Loan	66,986	46,673
Substandard | Commercial and Industrial
Financing Receivable, Recorded Investment [Line Items]
Loan	11,136	3,054
Substandard | Commercial Real Estate - Owner Occupied
Financing Receivable, Recorded Investment [Line Items]
Loan	22,616	18,591
Substandard | Commercial Real Estate - Investor
Financing Receivable, Recorded Investment [Line Items]
Loan	33,234	25,028
Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loan	0	0
Doubtful | Commercial and Industrial
Financing Receivable, Recorded Investment [Line Items]
Loan	0	0
Doubtful | Commercial Real Estate - Owner Occupied
Financing Receivable, Recorded Investment [Line Items]
Loan	0	0
Doubtful | Commercial Real Estate - Investor
Financing Receivable, Recorded Investment [Line Items]
Loan	$ 0	$ 0