Loans and Allowance for Loan Losses - Non-Accrual Loans, Loans Still Accruing and Past Due 90 Days or More and Restructured Loans (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Receivables [Abstract]
Non-accrual loans	$ 21,788	$ 20,194	$ 22,093
Loans still accruing and past due 90 days or more	49	261	263
Troubled debt restructured loans	204	226
Total	$ 22,041	$ 20,681	$ 22,356