Shareholders' Equity - Reconciliation of Changes in Total Shareholders' Equity (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Equity [Abstract]
Beginning balance	$ 870,709
Net proceeds from the issuance of common stock	29,321
Exercise of stock options	39
Earned portion of non-vested stock	1,193	596
Stock option expense	36	57
Deferred compensation outside directors	30
Adjustment to redemption value on noncontrolling redeemable Operating Partnership units	(1,628)
Net income attributable to common shareholders	16,673	14,280
Change in fair value of derivatives	(1,929)	1,539
Dividends	(22,111)
Ending balance	$ 892,333