Income Taxes - Reconciliation of Net Income to Taxable Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Net income available to the Company	$ 80,623	$ 215,120	$ 110,534
Add (subtract) net loss (income) of taxable REIT subsidiaries	(213)	(4,088)	(26,842)
Adjusted net income available to the Company	80,410	211,032	83,692
Book/tax depreciation difference	584	(5,104)	(3,770)
Book/tax difference in gain/loss transactions	628	(44,839)	(28,306)
Book/tax difference on stock-based compensation	(3,373)	(8,657)	(1,810)
Book/tax difference relating to change in tax regulations	(6,705)	(49,808)
Other book/tax differences, net	1,797	2,910	6,068
Taxable income of the Company before allocation of taxable capital gains	73,341	105,534	55,874
Income taxable as capital gains	(2,100)	(117,551)
Taxable ordinary income (loss) of the Company	$ 71,241	$ (12,017)	$ 55,874