Joint Ventures - Condensed Balance Sheets (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Liabilities and equity:
Equity	$ 1,682,316	$ 1,605,492
Total liabilities and shareholders' equity	3,089,823	2,989,279
Consolidated Joint Venture [Member]
Assets:
Cash	335	1,069
Other assets	0	37
Assets related to consolidated variable interest entity	335	1,106
Liabilities and equity:
Accrued expenses	290	487
Equity	45	619
Total liabilities and shareholders' equity	$ 335	$ 1,106