Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Taxes [Line Items]
Income tax expense	$ 7,000,000	$ 5,000,000
Built in gain tax	1,000,000
Income tax expense offset by deferred tax benefit	1,000,000	5,000,000
U.S. Federal Tax [Member] | REIT [Member]
Income Taxes [Line Items]
Income tax expense	$ 0	$ 0