Joint Ventures - Condensed Balance Sheets (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Assets:
Cash	$ 529,313	$ 396,619	$ 364,494	$ 425,316
Liabilities and equity:
Equity	1,535,777	1,304,441
Total liabilities and shareholders' equity	2,918,087	2,643,943
Consolidated Joint Venture
Assets:
Cash	1,199	1,214
Other assets	44	37
Total assets	1,243	1,251
Liabilities and equity:
Accrued expenses	542	550
Equity	701	701
Total liabilities and shareholders' equity	$ 1,243	$ 1,251