Summary of Stock Option Activity under Plan (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Options outstanding
Options outstanding, beginning of period	411,794	438,394	484,694
Granted
Exercised
Forfeited	(15,250)	(4,200)	(13,300)
Expired	(65,370)	(22,400)	(33,000)
Options outstanding, end of period	331,174	411,794	438,394
Options exercisable, end of period	318,279	378,004	378,710
Options unvested, end of period	12,895	33,790	59,684
Options outstanding, weighted Average Exercise Price
Options outstanding, beginning of period	$ 39.04	$ 38.76	$ 39.43
Granted
Exercised
Forfeited	$ 42.45	$ 35.54	$ 37.98
Expired	$ 36.56	$ 34.25	$ 48.85
Options outstanding, end of period	$ 39.37	$ 39.04	$ 38.76
Options exercisable, end of period	$ 40.62	$ 41.00	$ 41.66
Options unvested, end of period	$ 8.64	$ 17.17	$ 20.36
Options outstanding
Options outstanding, end of period	2 years 2 months 12 days	2 years 9 months 18 days	3 years 7 months 6 days
Options exercisable, end of period	2 years 1 month 6 days	2 years 6 months	3 years 1 month 6 days
Options unvested, end of period	5 years	5 years 4 months 24 days	6 years 1 month 6 days
Options outstanding, end of period, aggregate intrinsic value
Options outstanding, end of period	$ 1,708	$ 766	$ 1,143
Options exercisable, end of period	1,373	459	457
Options unvested, end of period	$ 335	$ 307	$ 686