Segment Financial Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 30, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 30, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Information [Line Items]
Net Interest Income	$ 16,594	$ 16,393	$ 16,649	$ 16,612	$ 16,407	$ 16,203	$ 16,264	$ 15,107	$ 66,248	$ 63,981	$ 48,671
Net Gains on Sales of Loans									3,234	2,381	2,160
Net Gains on Securities									1,667	3,024	0
Trust and Investment Product Fees									2,657	2,145	1,582
Insurance Revenues									5,524	5,819	5,347
Noncash Items:
Provision for Loan Losses									2,412	6,800	5,225
Depreciation and Amortization									4,688	5,139	3,720
Income Tax Benefit									10,669	7,726	5,623
Segment Profit (Loss)	6,194	6,292	5,967	5,602	5,573	5,167	4,864	4,645	24,055	20,249	13,405
Segment Assets									2,006,300	1,873,767	1,375,888
Core Banking [Member]
Segment Reporting Information [Line Items]
Net Interest Income									68,311	66,099	50,460
Net Gains on Sales of Loans									3,234	2,381	2,160
Net Gains on Securities									1,667	2,089	0
Trust and Investment Product Fees									5	3	2
Insurance Revenues									23	67	61
Noncash Items:
Provision for Loan Losses									2,412	6,800	5,225
Depreciation and Amortization									4,099	4,481	2,865
Income Tax Benefit									11,999	9,171	7,181
Segment Profit (Loss)									25,118	20,855	15,325
Segment Assets									2,006,992	1,875,417	1,368,348
Trust and Investment Advisory Services [Member]
Segment Reporting Information [Line Items]
Net Interest Income									21	16	8
Net Gains on Sales of Loans									0	0	0
Net Gains on Securities									0	0	0
Trust and Investment Product Fees									2,657	2,147	1,585
Insurance Revenues									36	13	26
Noncash Items:
Provision for Loan Losses									0	0	0
Depreciation and Amortization									24	26	29
Income Tax Benefit									(187)	(353)	(259)
Segment Profit (Loss)									(298)	(545)	(385)
Segment Assets									11,551	11,801	2,193
Insurance [Member]
Segment Reporting Information [Line Items]
Net Interest Income									34	22	27
Net Gains on Sales of Loans									0	0	0
Net Gains on Securities									0	0	0
Trust and Investment Product Fees									0	0	0
Insurance Revenues									5,465	5,755	5,282
Noncash Items:
Provision for Loan Losses									0	0	0
Depreciation and Amortization									415	482	826
Income Tax Benefit									181	272	(56)
Segment Profit (Loss)									250	352	(130)
Segment Assets									8,333	7,948	8,426
Other [Member]
Segment Reporting Information [Line Items]
Net Interest Income									(2,118)	(2,156)	(1,824)
Net Gains on Sales of Loans									0	0	0
Net Gains on Securities									0	935	0
Trust and Investment Product Fees									(5)	(5)	(5)
Insurance Revenues									0	(16)	(22)
Noncash Items:
Provision for Loan Losses									0	0	0
Depreciation and Amortization									150	150	0
Income Tax Benefit									(1,324)	(1,364)	(1,243)
Segment Profit (Loss)									(1,015)	(413)	(1,405)
Segment Assets									$ (20,576)	$ (21,399)	$ (3,079)