Capital Stock - Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator:
Net income available to common shareholders	$ 87,888	$ 147,361	$ 228,966	$ 485,675
Effect of dilutive securities:	0	0	0	0
Dilutive net income available to common shareholders	$ 87,888	$ 147,361	$ 228,966	$ 485,675
Denominator:
Weighted average basic shares (shares)	187,158,167	187,006,777	187,141,377	187,182,932
Effect of dilutive securities (shares)	1,282,004	578,181	1,189,732	522,899
Weighted average dilutive shares (shares)	188,440,171	187,584,958	188,331,109	187,705,831
Net income per average share attributable to common stockholders - Basic (usd per share)	$ 0.47	$ 0.79	$ 1.22	$ 2.59
Net income per average share attributable to common stockholders - Diluted (usd per share)	$ 0.47	$ 0.79	$ 1.22	$ 2.59