Shareholders' Equity - Reconciliation of Changes in Parent Company's Total Shareholders' Equity (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Equity [Abstract]
Beginning balance			$ 2,088,494
Net proceeds from the issuance of common stock through Dividend Reinvestment Plan			9,760
Earned portion of non-vested stock			3,246
Stock option expense			8
Deferred compensation - directors			0
Adjustment to redemption value on noncontrolling redeemable Operating Partnership units			1,380
Net income attributable to common shareholders	$ 19,355	$ 43,456	39,785	$ 71,796
Amortization of terminated hedge included in AOCL			458
Change in fair value of derivatives			1,400
Dividends			(90,231)
Ending balance	$ 2,054,300		$ 2,054,300