Shareholders' Equity - Reconciliation of Changes in Parent Company's Total Shareholders' Equity (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Equity [Abstract]
Beginning balance	$ 2,028,323
Earned portion of non-vested stock	1,495
Stock option expense	4
Adjustment to redemption value on noncontrolling redeemable Operating Partnership units	1,470
Net income attributable to common shareholders	33,889	$ 20,429
Amortization of terminated hedge included in AOCL	229
Change in fair value of derivatives	48
Dividends	(46,121)
Ending balance	$ 2,019,337