Shareholders' Equity Reconciliation of Weighted Average Number of Shares (Detail) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Equity [Abstract]
Weighted average number of common shares outstanding	63,902	65,592	64,263	65,909
Director Plan and deferred stock units	143	212	168	221
ESOP	106	108	104	92
Common shares outstanding—basic	64,151	65,912	64,535	66,222
Dilutive effect of Option Plans and Omnibus Plan	876	1,456	900	1,559
Common and potential common shares outstanding—diluted	65,027	67,368	65,435	67,781