Common Equity and Earnings per Share - Schedule of Weighted Average of Potential Class A Common Stock Excluded from Computation of Earnings Per Share (Detail) - Class A - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Class of Stock
Weighted shares of potential class A stock excluded from calculation of diluted earnings per share	3,723	1,476	3,572	1,536
2025 Convertible Notes
Class of Stock
Weighted shares of potential class A stock excluded from calculation of diluted earnings per share	1,633	0	1,633	0
2027 Convertible Notes
Class of Stock
Weighted shares of potential class A stock excluded from calculation of diluted earnings per share	733	0	601	0
Stock Options
Class of Stock
Weighted shares of potential class A stock excluded from calculation of diluted earnings per share	1,252	1,476	1,246	1,536
RSU
Class of Stock
Weighted shares of potential class A stock excluded from calculation of diluted earnings per share	103	0	91	0
Employee Stock Purchase Plan
Class of Stock
Weighted shares of potential class A stock excluded from calculation of diluted earnings per share	2	0	1	0