Changes in Issued and Outstanding Common Shares (Detail) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity [Abstract]
Beginning Balance	29,507,000	29,124,000	28,862,000
Net Vested Stock Grants	230,000	343,000	220,000
Employee Stock Purchase Plan	45,000	40,000	42,000
Ending Balance	29,782,000	29,507,000	29,124,000