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, 2011	Dec. 31, 2010	Dec. 31, 2009
Beginning balance				15,742,000				16,846,000		15,742,000	16,846,000	16,856,000
Vested stock grants										178,000	109,000	74,000
Employee stock purchase plan										19,074	22,000	17,000
Stock options exercised										52,250	29,000	40,750
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	14,012,000				15,742,000				16,846,000	14,012,000	15,742,000	16,846,000