Real Estate and Accumulated Depreciation - Changes in Total Real Estate Investments and Related Accumulated Depreciation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Total real estate investments:
Balance, beginning of year	$ 1,948,165	$ 1,803,200	$ 1,700,813
Acquisitions	0	48,579	77,258
Improvements	135,966	98,917	42,640
Retirements	(2,534)	(2,531)	(17,511)
Balance, end of year	2,081,597	1,948,165	1,803,200
Total accumulated depreciation:
Balance, beginning of year	525,518	488,166	458,279
Depreciation expense	40,490	39,768	40,197
Retirements	(2,534)	(2,416)	(10,310)
Balance, end of year	$ 563,474	$ 525,518	$ 488,166