Shareholders' Equity Reconciliation of Weighted Average Number of Shares (Detail) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Equity [Abstract]
Weighted average number of common shares outstanding	61,300	61,100	61,300	61,100
Director Plan and deferred stock units	200	200	200	200
ESOP	100	100	200	100
Common shares outstanding—basic	61,600	61,400	61,700	61,400
Dilutive effect of Omnibus Plan	0	800	0	700
Common and potential common shares outstanding—diluted	61,600	62,200	61,700	62,100