Changes in Issued and Outstanding Common Shares (Detail) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Equity [Abstract]
Beginning balance	28,862,000	28,562,000	28,396,000
Vested stock grants	220,000	254,000	118,000
Employee stock purchase plan	41,224	41,714	38,000
Stock options exercised		1,500	5,250
Ending balance	29,124,000	28,862,000	28,562,000