Loans Receivable and Allowance for Loan Losses (Narrative) (Detail)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) Contract SecurityLoan troubled_debt_restructuring borrower	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) SecurityLoan	Dec. 31, 2015 USD ($) Contract SecurityLoan troubled_debt_restructuring borrower	Sep. 30, 2015 SecurityLoan	May 30, 2014 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Principal amount of nonaccrual loans	$ 40,000,000		$ 40,000,000		$ 40,000,000	$ 44,400,000
Loans less than 90 days past due	5,400,000		$ 5,400,000		5,400,000	$ 18,300,000
Number of loans 90 days past due and still accruing | Contract			0			1
Recorded Investment greater than 90 days accruing	0		$ 0		0	$ 165,000
Impaired loan defined floor limit (greater than)	1,000,000.0		$ 1,000,000.0		1,000,000.0
Impaired loans number | SecurityLoan			139			148
Impaired loans	44,415,000		$ 44,415,000		44,415,000	$ 50,867,000
Number of troubled debt restructurings | troubled_debt_restructuring			115			122
Number of borrowers | borrower			114			120
Loans and leases receivable, impaired, nonperforming, accrual of interest	21,100,000		$ 21,100,000		$ 21,100,000	$ 26,000,000
Charge off, impaired loan		$ 312,000		$ 312,000
Weighted average modified interest rate		3.00%		5.26%
Weighted average prior modification rate		3.00%		5.71%
Number of payment defaults for loans modified as TDRs | SecurityLoan					0		0
Interest income	76,045,000	$ 73,013,000	224,824,000	$ 217,432,000
Average balance of impaired loans			45,476,000			51,225,000
Team Capital Bank [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of acquired loans								$ 5,200,000
Decrease in PCI loans			1,700,000
Balance of PCI loans	1,700,000		1,700,000		$ 1,700,000	3,400,000
Interest income	179,000	129,000	682,000	349,000
Impaired Loans Troubled Debt Restructurings [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Allowances for loan losses		$ 0		$ 82,000
With Related Allowance For Loan Losses [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Allowances for loan losses	2,127,000		2,127,000		2,127,000	2,271,000
Loans With No Related Allowance [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Allowances for loan losses	0		0		0	0
Impaired financing receivable with no related allowance	$ 28,480,000		28,480,000		$ 28,480,000
Average balance of impaired loans			$ 29,268,000			33,245,000
Loans With No Related Allowance [Member] | No Allowance For Loan Losses Required [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired financing receivable with no related allowance						$ 33,376,000