Capital Stock (Detail) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Class Of Stock [Line Items]
Beginning balance	169,316,460	168,628,177	163,342,894
Stock options/SARs exercised	0	77,002	195,242
Restricted stock grants	490,609	335,103	270,062
Restricted stock units vested	266,541	252,507	244,413
Shares retired	(739)	0	0
Treasury shares	28,736	23,671	15,566
Ending balance	247,144,356	169,316,460	168,628,177
MRD
Class Of Stock [Line Items]
MRD Merger	77,042,749	0	0
Common Stock
Class Of Stock [Line Items]
Equity offering	77,799,000	665,000	5,270,000
Common Stock | Equity Offering
Class Of Stock [Line Items]
Equity offering	0	0	4,560,000