Loans Receivable and Allowance for Loan Losses (Narrative) (Detail)	3 Months Ended		12 Months Ended
	Mar. 31, 2016 USD ($) SecurityLoan troubled_debt_restructuring Contract borrower	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($) SecurityLoan troubled_debt_restructuring Contract borrower	May. 30, 2014 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Principal amount of nonaccrual loans	$ 50,600,000		$ 44,400,000
Loans less than 90 days past due	$ 13,100,000		$ 18,300,000
Number of loans 90 days past due and still accruing | Contract	0		1
Recorded Investment greater than 90 days accruing	$ 0		$ 165,000
Impaired loan defined floor limit (greater than)	$ 1,000,000.0
Impaired loans number | SecurityLoan	151		148
Impaired loans	$ 54,193,000		$ 50,867,000
Number of troubled debt restructurings | troubled_debt_restructuring	119		122
Number of borrowers | borrower	117		120
Loans and leases receivable, impaired, nonperforming, accrual of interest	$ 25,100,000		$ 26,000,000
Weighted average modified interest rate		5.90%
Weighted average prior modification rate		5.83%
Interest income	73,974,000	$ 72,231,000
Average balance of impaired loans	54,500,000		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				$ 5,220,000
Decrease in PCI loans	750,000
Balance of PCI loans	2,700,000		3,400,000
Interest income	280,000	76,000
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			33,400,000
With Related Allowance For Loan Losses [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Allowances for loan losses	$ 5,100,000		$ 2,300,000
Impaired Loans Troubled Debt Restructurings [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Allowances for loan losses		$ 31,000