Loans - Investment in Loans by Portfolio Segment and Based on Impairment (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance, Beginning balance	$ 18,264,000	$ 19,037,000	$ 21,116,000	$ 21,130,000
Provision (recovery)	116,000	657,000	(1,465,000)	3,834,000
Chargeoffs	(667,000)	(1,104,000)	(3,023,000)	(7,854,000)
Recoveries	419,000	2,442,000	1,504,000	3,922,000
Allowance, Ending balance	18,132,000	21,032,000	18,132,000	21,032,000
Loans individually evaluated for impairment	3,632,000	2,423,000	3,632,000	2,423,000	3,325,000
Loans collectively evaluated for impairment	14,500,000		14,500,000		17,791,000
Allowance, Ending balance	18,132,000		18,132,000		21,116,000
Loans individually evaluated for impairment	47,279,000	46,327,000	47,279,000	46,327,000	48,181,000
Loans collectively evaluated for impairment	1,089,912,000		1,089,912,000		1,000,984,000
Ending balance	1,137,191,000		1,137,191,000		1,049,165,000
Commercial Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance, Beginning balance	957,000	903,000	739,000	1,448,000
Provision (recovery)	(109,000)	(223,000)	(246,000)	(843,000)
Chargeoffs		(16,000)	(45,000)	(144,000)
Recoveries	158,000	180,000	558,000	383,000
Allowance, Ending balance	1,006,000	844,000	1,006,000	844,000
Loans individually evaluated for impairment	3,000		3,000
Loans collectively evaluated for impairment	1,003,000		1,003,000		739,000
Allowance, Ending balance	1,006,000		1,006,000		739,000
Loans individually evaluated for impairment	4,029,000		4,029,000		4,044,000
Loans collectively evaluated for impairment	35,824,000		35,824,000		22,097,000
Ending balance	39,853,000		39,853,000		26,141,000
Permanent Real Estate Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance, Beginning balance	12,353,000	12,129,000	13,794,000	13,819,000
Provision (recovery)	409,000	2,286,000	(352,000)	5,064,000
Chargeoffs	(338,000)	(651,000)	(1,365,000)	(5,794,000)
Recoveries	51,000	92,000	398,000	767,000
Allowance, Ending balance	12,475,000	13,856,000	12,475,000	13,856,000
Loans individually evaluated for impairment	2,368,000	1,222,000	2,368,000	1,222,000	1,786,000
Loans collectively evaluated for impairment	10,107,000		10,107,000		12,008,000
Allowance, Ending balance	12,475,000		12,475,000		13,794,000
Loans individually evaluated for impairment	27,871,000		27,871,000		27,224,000
Loans collectively evaluated for impairment	830,591,000		830,591,000		753,220,000
Ending balance	858,462,000		858,462,000		780,444,000
Construction Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance, Beginning balance	1,164,000	1,803,000	2,281,000	1,404,000
Provision (recovery)	(143,000)	(1,800,000)	(851,000)	(1,354,000)
Chargeoffs	(100,000)	(37,000)	(530,000)	(402,000)
Recoveries	10,000	1,913,000	31,000	2,231,000
Allowance, Ending balance	931,000	1,879,000	931,000	1,879,000
Loans individually evaluated for impairment	203,000	677,000	203,000	677,000	680,000
Loans collectively evaluated for impairment	728,000		728,000		1,601,000
Allowance, Ending balance	931,000		931,000		2,281,000
Loans individually evaluated for impairment	2,453,000		2,453,000		3,092,000
Loans collectively evaluated for impairment	54,949,000		54,949,000		50,257,000
Ending balance	57,402,000		57,402,000		53,349,000
Consumer Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance, Beginning balance	3,790,000	4,202,000	4,302,000	4,459,000
Provision (recovery)	(41,000)	394,000	(16,000)	967,000
Chargeoffs	(229,000)	(400,000)	(1,083,000)	(1,514,000)
Recoveries	200,000	257,000	517,000	541,000
Allowance, Ending balance	3,720,000	4,453,000	3,720,000	4,453,000
Loans individually evaluated for impairment	1,058,000	524,000	1,058,000	524,000	859,000
Loans collectively evaluated for impairment	2,662,000		2,662,000		3,443,000
Allowance, Ending balance	3,720,000		3,720,000		4,302,000
Loans individually evaluated for impairment	12,926,000		12,926,000		13,821,000
Loans collectively evaluated for impairment	168,548,000		168,548,000		175,410,000
Ending balance	$ 181,474,000		$ 181,474,000		$ 189,231,000