Capital Stock (Detail) - shares	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Class Of Stock [Line Items]
Beginning balance	168,628,177	163,342,894
Restricted stock grants	324,294	270,062
Restricted stock units vested	243,601	244,413
Treasury shares issued	20,443	15,566
Ending balance	169,293,504	168,628,177
Common Stock | Equity Offering
Class Of Stock [Line Items]
Equity offering	0	4,560,000
Stock Appreciation Rights (SARs)
Class Of Stock [Line Items]
SARs exercised	76,989	195,242