Loans, Allowance for Loan and Lease Losses, and Reserve for Off-Balance Sheet Credit Commitments (Detail 5) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Recorded Investment
With no related allowance recorded	$ 36,921	$ 77,958	$ 45,611
With an allowance recorded	15,127	22,788	15,611
Total impaired loans	52,048	100,746	61,222
Unpaid Contractual Principal Balance
With no related allowance recorded	41,541	98,320	51,987
With an allowance recorded	20,726	25,397	18,352
Total impaired loans	62,267	123,717	70,339
Related Allowance
Total impaired loans	784	2,857	728
Average Recorded Investment
With no related allowance recorded	41,266	78,714
With an allowance recorded	15,369	21,991
Total impaired loans	56,635	100,705
Interest Income Recognized
With no related allowance recorded	285	688
With an allowance recorded	114	44
Total impaired loans	399	732
Commercial
Recorded Investment
With no related allowance recorded	1,449	11,257	8,894
With an allowance recorded	6,151	17,426	6,470
Total impaired loans	7,600	28,683	15,364
Unpaid Contractual Principal Balance
With no related allowance recorded	1,637	11,920	9,182
With an allowance recorded	11,425	19,663	8,878
Total impaired loans	13,062	31,583	18,060
Related Allowance
Total impaired loans	471	2,557	399
Average Recorded Investment
With no related allowance recorded	5,172	14,489
With an allowance recorded	6,310	15,781
Total impaired loans	11,482	30,270
Interest Income Recognized
With no related allowance recorded	5	137
With an allowance recorded	17
Total impaired loans	22	137
Commercial real estate mortgages
Recorded Investment
With no related allowance recorded	17,838	36,562	19,858
With an allowance recorded	5,041	5,362	5,184
Total impaired loans	22,879	41,924	25,042
Unpaid Contractual Principal Balance
With no related allowance recorded	18,762	39,660	22,416
With an allowance recorded	5,375	5,734	5,526
Total impaired loans	24,137	45,394	27,942
Related Allowance
Total impaired loans	273	300	281
Average Recorded Investment
With no related allowance recorded	18,848	34,666
With an allowance recorded	5,113	5,373
Total impaired loans	23,961	40,039
Interest Income Recognized
With no related allowance recorded	208	438
With an allowance recorded	71	44
Total impaired loans	279	482
Residential mortgages
Recorded Investment
With no related allowance recorded	7,720	7,904	7,980
With an allowance recorded	3,935		3,957
Total impaired loans	11,655	7,904	11,937
Unpaid Contractual Principal Balance
With no related allowance recorded	7,980	8,669	8,256
With an allowance recorded	3,926		3,948
Total impaired loans	11,906	8,669	12,204
Related Allowance
Total impaired loans	40		48
Average Recorded Investment
With no related allowance recorded	7,850	7,721
With an allowance recorded	3,946	837
Total impaired loans	11,796	8,558
Interest Income Recognized
With no related allowance recorded	10	24
With an allowance recorded	26
Total impaired loans	36	24
Fixed
Recorded Investment
With no related allowance recorded	7,720	4,888	7,756
Unpaid Contractual Principal Balance
With no related allowance recorded	7,980	5,051	7,994
Average Recorded Investment
With no related allowance recorded	7,738	3,512
Interest Income Recognized
With no related allowance recorded	10	10
Variable
Recorded Investment
With no related allowance recorded		3,016	224
With an allowance recorded	3,935		3,957
Unpaid Contractual Principal Balance
With no related allowance recorded		3,618	262
With an allowance recorded	3,926		3,948
Related Allowance
Total impaired loans	40		48
Average Recorded Investment
With no related allowance recorded	112	4,209
With an allowance recorded	3,946	837
Interest Income Recognized
With no related allowance recorded		14
With an allowance recorded	26
Real estate construction
Recorded Investment
With no related allowance recorded	8,979	18,788	6,609
Total impaired loans	8,979	18,788	6,609
Unpaid Contractual Principal Balance
With no related allowance recorded	11,119	33,566	8,758
Total impaired loans	11,119	33,566	8,758
Average Recorded Investment
With no related allowance recorded	7,794	18,942
Total impaired loans	7,794	18,942
Interest Income Recognized
With no related allowance recorded	62	89
Total impaired loans	62	89
Construction
Recorded Investment
With no related allowance recorded		5,484
Unpaid Contractual Principal Balance
With no related allowance recorded		6,766
Average Recorded Investment
With no related allowance recorded		5,484
Interest Income Recognized
With no related allowance recorded		55
Land.
Recorded Investment
With no related allowance recorded	8,979	13,304	6,609
Unpaid Contractual Principal Balance
With no related allowance recorded	11,119	26,800	8,758
Average Recorded Investment
With no related allowance recorded	7,794	13,458
Interest Income Recognized
With no related allowance recorded	62	34
Home equity loans and lines of credit
Recorded Investment
With no related allowance recorded	935	3,447	2,270
Total impaired loans	935	3,447	2,270
Unpaid Contractual Principal Balance
With no related allowance recorded	2,043	4,505	3,375
Total impaired loans	2,043	4,505	3,375
Average Recorded Investment
With no related allowance recorded	1,602	2,888
Total impaired loans	1,602	2,888
Installment
Average Recorded Investment
With no related allowance recorded		8
Total impaired loans		8
Consumer Installment loan
Average Recorded Investment
With no related allowance recorded		$ 8