Capital Stock (Detail) - shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Class Of Stock [Line Items]
Beginning balance	168,628,177	163,342,894	162,514,098
Stock options/SARs exercised	77,002	195,242	278,916
Restricted stock grants	335,103	270,062	401,122
Restricted stock units vested	252,507	244,413	119,480
Treasury shares	23,671	15,566	29,278
Ending balance	169,316,460	168,628,177	163,342,894
Common Stock
Class Of Stock [Line Items]
Equity offering	665,000	5,270,000	799,000
Common Stock | Equity Offering
Class Of Stock [Line Items]
Equity offering	0	4,560,000	0