Shareholders' Equity Reconciliation of Weighted Average Number of Shares (Detail) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Equity [Abstract]
Weighted average number of common shares outstanding	65,592	65,988	65,909	65,771
Director Plan and deferred stock units	212	201	221	204
ESOP	108	72	92	76
Common shares outstanding—basic	65,912	66,261	66,222	66,051
Dilutive effect of Option Plans and Omnibus Plan	1,456	2,067	1,559	2,074
Common and potential common shares outstanding—diluted	67,368	68,328	67,781	68,125