Capital Stock (Detail) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Class Of Stock [Line Items]
Beginning balance	248,129,430	247,144,356	169,316,460
Restricted stock grants	865,095	539,096	490,609
Shares retired			(739)
Treasury shares	5,302	15,580	28,736
Ending balance	249,510,022	248,129,430	247,144,356
MRD
Class Of Stock [Line Items]
MRD Merger			77,042,749
Restricted Stock
Class Of Stock [Line Items]
Restricted stock units vested	434,046	344,937	266,541
Performance Share
Class Of Stock [Line Items]
Performance stock units issued	76,149	85,461