Joint Ventures - Condensed Balance Sheets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Assets:
Cash	$ 667,863	$ 396,619	$ 425,316	$ 545,419
Liabilities and equity:
Equity	1,605,492	1,304,441	$ 1,239,165	$ 1,124,255
Total liabilities and shareholders' equity	2,989,279	2,643,943
Consolidated Joint Venture
Assets:
Cash	1,069	1,214
Other assets	37	37
Total assets	1,106	1,251
Liabilities and equity:
Accrued expenses	487	550
Equity	619	701
Total liabilities and shareholders' equity	$ 1,106	$ 1,251