Loans Receivable, Net - Risk Category of Loans by Loan Portfolio Segment Excluding PCI Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loan	$ 3,158,032	$ 1,943,444
Commercial Real Estate - Owner Occupied
Financing Receivable, Recorded Investment [Line Items]
Loan	762,641	569,497
Commercial Real Estate - Investor
Financing Receivable, Recorded Investment [Line Items]
Loan	2,025,551	1,186,302
Commercial and Industrial
Financing Receivable, Recorded Investment [Line Items]
Loan	369,840	187,645
Pass
Financing Receivable, Recorded Investment [Line Items]
Loan	3,091,746	1,874,637
Pass | Commercial Real Estate - Owner Occupied
Financing Receivable, Recorded Investment [Line Items]
Loan	744,157	546,569
Pass | Commercial Real Estate - Investor
Financing Receivable, Recorded Investment [Line Items]
Loan	1,984,332	1,146,630
Pass | Commercial and Industrial
Financing Receivable, Recorded Investment [Line Items]
Loan	363,257	181,438
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loan	24,215	22,134
Special Mention | Commercial Real Estate - Owner Occupied
Financing Receivable, Recorded Investment [Line Items]
Loan	3,150	4,337
Special Mention | Commercial Real Estate - Investor
Financing Receivable, Recorded Investment [Line Items]
Loan	17,216	14,644
Special Mention | Commercial and Industrial
Financing Receivable, Recorded Investment [Line Items]
Loan	3,849	3,153
Substandard
Financing Receivable, Recorded Investment [Line Items]
Loan	40,466	46,673
Substandard | Commercial Real Estate - Owner Occupied
Financing Receivable, Recorded Investment [Line Items]
Loan	15,334	18,591
Substandard | Commercial Real Estate - Investor
Financing Receivable, Recorded Investment [Line Items]
Loan	23,073	25,028
Substandard | Commercial and Industrial
Financing Receivable, Recorded Investment [Line Items]
Loan	2,059	3,054
Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loan	1,605	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	930	0
Doubtful | Commercial and Industrial
Financing Receivable, Recorded Investment [Line Items]
Loan	$ 675	$ 0