Capital Stock - Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net income available to common shareholders	$ 111,880	$ 87,888	$ 40,322	$ 100,755	$ (117,235)	$ 147,361	$ 108,708	$ 229,607	$ 340,847	$ 368,440	$ 491,184
Effect of dilutive securities:									0	0	0
Dilutive net income available to common shareholders									$ 340,847	$ 368,440	$ 491,184
Denominator:
Weighted average basic shares (shares)									187,156,990	187,146,170	187,780,355
Effect of dilutive securities (shares)									1,249,454	602,692	506,965
Weighted average dilutive shares (shares)									188,406,444	187,748,862	188,287,320
Net income per average share attributable to common stockholders - Basic (usd per share)	$ 0.60	$ 0.47	$ 0.22	$ 0.54	$ (0.63)	$ 0.79	$ 0.58	$ 1.22	$ 1.82	$ 1.97	$ 2.62
Net income per average share attributable to common stockholders - Diluted (usd per share)									$ 1.81	$ 1.96	$ 2.61