Shareholders' Equity Reconciliation of Weighted Average Number of Shares (Detail) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Equity [Abstract]
Weighted average number of common shares outstanding	66,000	65,769	66,068	65,663
Director Plan and deferred stock units	242	209	224	205
ESOP	82	82	84	78
Common shares outstanding—basic	66,324	66,060	66,376	65,946
Dilutive effect of Option Plans and Omnibus Plan	1,505	2,028	1,611	2,077
Common and potential common shares outstanding—diluted	67,829	68,088	67,987	68,023