Changes in Issued and Outstanding Common Shares (Detail)	3 Months Ended									12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2009	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Beginning balance				15,742,000						14,047,000	13,956,000	15,742,000
Vested stock grants										50,000	60,000	122,000
Employee stock purchase plan										17,640	16,000	19,000
Stock options exercised										83,500	15,000	52,250
Treasury shares purchased	(376,911)	(749,076)	(597,026)	(256,094)	(35,566)	(97,115)	(558,003)	(573,600)	(141,576)			(1,979,107)	(1,264,284)	(141,576)
Ending balance	13,956,000				15,742,000					14,198,000	14,047,000	13,956,000	15,742,000