Shareholders' Equity Reconciliation of Weighted Average Number of Shares (Detail) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Equity [Abstract]
Weighted average number of common shares outstanding	61,500	61,200	61,400	61,100
Director Plan and deferred stock units	200	200	200	200
ESOP	200	100	200	100
Common shares outstanding—basic	61,900	61,500	61,800	61,400
Dilutive effect of Omnibus Plan	900	800	0	800
Common and potential common shares outstanding—diluted	62,800	62,300	61,800	62,200