Summary of Significant Accounting Policies - Calculation of Both Basic and Diluted Earnings Per Common 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
Earnings Per Common Share:
Net income available to common shareholders	$ 34,932	$ 78,719	$ 73,296	$ 110,158	$ 73,930	$ 66,387	$ 69,630	$ 38,793	$ 297,105	$ 248,740	$ 152,458
Basic weighted-average number of common shares outstanding (in shares)	355,821,005	331,797,982	331,748,552	331,601,260	331,492,648	331,486,500	331,318,381	330,727,416	337,792,270	331,258,964	264,038,123
Plus: Common stock equivalents (in shares)									2,325,538	1,434,754	850,884
Diluted weighted-average number of common shares outstanding (in shares)	358,864,876	333,405,196	332,959,802	332,834,466	332,856,385	333,000,242	332,895,483	332,465,527	340,117,808	332,693,718	264,889,007
Earnings per common share:
Basic (in usd per share)	$ 0.10	$ 0.24	$ 0.22	$ 0.33	$ 0.22	$ 0.20	$ 0.21	$ 0.12	$ 0.88	$ 0.75	$ 0.58
Diluted (in usd per share)	$ 0.10	$ 0.24	$ 0.22	$ 0.33	$ 0.22	$ 0.20	$ 0.21	$ 0.12	$ 0.87	$ 0.75	$ 0.58