Loans and the Allowance for Credit Losses - Summary of Age Analysis of Loan Categories (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment [Line Items]
Current	$ 3,902,856	$ 3,848,624
30-59 Days Past Due	8,390	10,041
60-89 Days Past Due	5,084	9,152
90 Days or More Past Due	29,788	27,100
Total Past Due	43,262	46,293
Total Loans	3,946,118	3,894,917
90 Days or More Past Due and Accruing	2,947	2,591
Loans held for sale	10,641	5,855
Total loans, current	3,913,497	3,854,479
Total loans	3,956,759	3,900,772
Loans Held for Sale [Member]
Financing Receivable, Recorded Investment [Line Items]
30-59 Days Past Due
60-89 Days Past Due
90 Days or More Past Due
Total Past Due
90 Days or More Past Due and Accruing
Loans held for sale, Current	10,641	5,855
Loans held for sale	10,641	5,855
Commercial Real Estate - Land and Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	253,610	261,165
30-59 Days Past Due	290	2
60-89 Days Past Due	1
90 Days or More Past Due	1,598	1,950
Total Past Due	1,889	1,952
Total Loans	255,499	263,117
90 Days or More Past Due and Accruing	248	248
Commercial Real Estate - Improved Property [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	1,669,880	1,632,973
30-59 Days Past Due	456	2,482
60-89 Days Past Due	967	2,346
90 Days or More Past Due	14,070	12,001
Total Past Due	15,493	16,829
Total Loans	1,685,373	1,649,802
90 Days or More Past Due and Accruing		318
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	1,923,490	1,894,138
30-59 Days Past Due	746	2,484
60-89 Days Past Due	968	2,346
90 Days or More Past Due	15,668	13,951
Total Past Due	17,382	18,781
Total Loans	1,940,872	1,912,919
90 Days or More Past Due and Accruing	248	566
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	574,121	552,414
30-59 Days Past Due	1,594	1,112
60-89 Days Past Due	229	977
90 Days or More Past Due	2,721	1,746
Total Past Due	4,544	3,835
Total Loans	578,665	556,249
90 Days or More Past Due and Accruing	6
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	884,456	875,192
30-59 Days Past Due	1,554	1,641
60-89 Days Past Due	2,692	4,710
90 Days or More Past Due	9,655	9,261
Total Past Due	13,901	15,612
Total Loans	898,357	890,804
90 Days or More Past Due and Accruing	1,843	1,289
Home Equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	291,075	281,004
30-59 Days Past Due	2,004	1,581
60-89 Days Past Due	666	470
90 Days or More Past Due	1,382	1,632
Total Past Due	4,052	3,683
Total Loans	295,127	284,687
90 Days or More Past Due and Accruing	628	411
Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	229,714	245,876
30-59 Days Past Due	2,492	3,223
60-89 Days Past Due	529	649
90 Days or More Past Due	362	510
Total Past Due	3,383	4,382
Total Loans	233,097	250,258
90 Days or More Past Due and Accruing	222	325
Non-Accrual Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	6,636	9,028
30-59 Days Past Due	1,694	588
60-89 Days Past Due	1,060	2,722
90 Days or More Past Due	26,728	24,295
Total Past Due	29,482	27,605
Total Loans	36,118	36,633
TDRs Accruing Interest [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	12,818	13,595
30-59 Days Past Due	167	171
60-89 Days Past Due	415	881
90 Days or More Past Due	113	214
Total Past Due	695	1,266
Total Loans	13,513	14,861
Total Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	19,454	22,623
30-59 Days Past Due	1,861	759
60-89 Days Past Due	1,475	3,603
90 Days or More Past Due	26,841	24,509
Total Past Due	30,177	28,871
Total Loans	$ 49,631	$ 51,494