Loans, Allowance for Loan and Lease Losses, and Reserve for Off-Balance Sheet Credit Commitments (Detail 5) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Recorded Investment
With no related allowance recorded	$ 37,605	$ 43,708	$ 37,605	$ 43,708	$ 45,611
With an allowance recorded	22,287	14,867	22,287	14,867	15,611
Total impaired loans	59,892	58,575	59,892	58,575	61,222
Unpaid Contractual Principal Balance
With no related allowance recorded	47,087	49,654	47,087	49,654	51,987
With an allowance recorded	26,539	17,691	26,539	17,691	18,352
Total impaired loans	73,626	67,345	73,626	67,345	70,339
Related Allowance
Total impaired loans	2,609	1,595	2,609	1,595	728
Average Recorded Investment
With no related allowance recorded	36,391	50,899	38,828	64,807
With an allowance recorded	18,778	23,196	17,074	22,593
Total impaired loans	55,169	74,095	55,902	87,400
Interest Income Recognized
With no related allowance recorded	315	343	883	1,387
With an allowance recorded	121	73	358	203
Total impaired loans	436	416	1,241	1,590
Commercial
Recorded Investment
With no related allowance recorded	4,784	6,653	4,784	6,653	8,894
With an allowance recorded	13,401	9,663	13,401	9,663	6,470
Total impaired loans	18,185	16,316	18,185	16,316	15,364
Unpaid Contractual Principal Balance
With no related allowance recorded	10,605	6,684	10,605	6,684	9,182
With an allowance recorded	17,347	12,134	17,347	12,134	8,878
Total impaired loans	27,952	18,818	27,952	18,818	18,060
Related Allowance
Total impaired loans	2,315	1,304	2,315	1,304	399
Average Recorded Investment
With no related allowance recorded	3,619	6,817	4,395	10,653
With an allowance recorded	9,869	15,957	8,090	15,869
Total impaired loans	13,488	22,774	12,485	26,522
Interest Income Recognized
With no related allowance recorded	71	38	94	205
With an allowance recorded	95		138
Total impaired loans	166	38	232	205
Commercial real estate mortgages
Recorded Investment
With no related allowance recorded	17,921	20,347	17,921	20,347	19,858
With an allowance recorded	4,997	5,204	4,997	5,204	5,184
Total impaired loans	22,918	25,551	22,918	25,551	25,042
Unpaid Contractual Principal Balance
With no related allowance recorded	19,095	22,698	19,095	22,698	22,416
With an allowance recorded	5,311	5,557	5,311	5,557	5,526
Total impaired loans	24,406	28,255	24,406	28,255	27,942
Related Allowance
Total impaired loans	255	291	255	291	281
Average Recorded Investment
With no related allowance recorded	17,947	24,290	18,398	29,478
With an allowance recorded	5,008	5,214	5,061	5,293
Total impaired loans	22,955	29,504	23,459	34,771
Interest Income Recognized
With no related allowance recorded	200	219	605	903
With an allowance recorded		73	142	191
Total impaired loans	200	292	747	1,094
Residential mortgages
Recorded Investment
With no related allowance recorded	7,961	7,785	7,961	7,785	7,980
With an allowance recorded	3,889		3,889		3,957
Total impaired loans	11,850	7,785	11,850	7,785	11,937
Unpaid Contractual Principal Balance
With no related allowance recorded	8,255	8,139	8,255	8,139	8,256
With an allowance recorded	3,881		3,881		3,948
Total impaired loans	12,136	8,139	12,136	8,139	12,204
Related Allowance
Total impaired loans	39		39		48
Average Recorded Investment
With no related allowance recorded	7,981	7,190	7,915	7,456
With an allowance recorded	3,901	2,000	3,923	1,419
Total impaired loans	11,882	9,190	11,838	8,875
Interest Income Recognized
With no related allowance recorded	14	50	40	98
With an allowance recorded	26		78	11
Total impaired loans	40	50	118	109
Fixed
Recorded Investment
With no related allowance recorded	7,961	2,015	7,961	2,015	7,756
Unpaid Contractual Principal Balance
With no related allowance recorded	8,255	2,254	8,255	2,254	7,994
Average Recorded Investment
With no related allowance recorded	7,981	3,406	7,859	3,459
Interest Income Recognized
With no related allowance recorded	14	10	40	30
Variable
Recorded Investment
With no related allowance recorded		5,770		5,770	224
With an allowance recorded	3,889		3,889		3,957
Unpaid Contractual Principal Balance
With no related allowance recorded		5,885		5,885	262
With an allowance recorded	3,881		3,881		3,948
Related Allowance
Total impaired loans	39		39		48
Average Recorded Investment
With no related allowance recorded		3,784	56	3,997
With an allowance recorded	3,901	2,000	3,923	1,419
Interest Income Recognized
With no related allowance recorded		40		68
With an allowance recorded	26		78	11
Real estate construction
Recorded Investment
With no related allowance recorded	5,802	6,610	5,802	6,610	6,609
Total impaired loans	5,802	6,610	5,802	6,610	6,609
Unpaid Contractual Principal Balance
With no related allowance recorded	6,885	8,758	6,885	8,758	8,758
Total impaired loans	6,885	8,758	6,885	8,758	8,758
Average Recorded Investment
With no related allowance recorded	5,809	9,728	6,801	14,335
Total impaired loans	5,809	9,728	6,801	14,335
Interest Income Recognized
With no related allowance recorded	28	35	142	180
Total impaired loans	28	35	142	180
Construction
Average Recorded Investment
With no related allowance recorded				2,742
Interest Income Recognized
With no related allowance recorded				76
Land.
Recorded Investment
With no related allowance recorded	5,802	6,610	5,802	6,610	6,609
Unpaid Contractual Principal Balance
With no related allowance recorded	6,885	8,758	6,885	8,758	8,758
Average Recorded Investment
With no related allowance recorded	5,809	9,728	6,801	11,593
Interest Income Recognized
With no related allowance recorded	28	35	142	104
Home equity loans and lines of credit
Recorded Investment
With no related allowance recorded	1,137	2,313	1,137	2,313	2,270
Total impaired loans	1,137	2,313	1,137	2,313	2,270
Unpaid Contractual Principal Balance
With no related allowance recorded	2,247	3,375	2,247	3,375	3,375
Total impaired loans	2,247	3,375	2,247	3,375	$ 3,375
Average Recorded Investment
With no related allowance recorded	1,035	2,874	1,319	2,881
Total impaired loans	1,035	2,874	1,319	2,881
Interest Income Recognized
With no related allowance recorded	2		2
Total impaired loans	$ 2		$ 2
Installment
Average Recorded Investment
With no related allowance recorded				4
With an allowance recorded		25		12
Total impaired loans		25		16
Interest Income Recognized
With no related allowance recorded		1		1
With an allowance recorded				1
Total impaired loans		1		2
Consumer Installment loan
Average Recorded Investment
With no related allowance recorded				4
With an allowance recorded		25		12
Interest Income Recognized
With no related allowance recorded		$ 1		1
With an allowance recorded				$ 1