Related Party Transactions - Additional Information (Detail) - USD ($) $ in Thousands				3 Months Ended		6 Months Ended
	Jun. 20, 2017	May 22, 2017	Jun. 18, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Related Party Transaction [Line Items]
Expense incurred as result of multiple service agreements				$ 2,800	$ 2,374	$ 5,507	$ 4,788
Interest expense accrued and/or paid due to intercompany arrangements				32		32
Interest income accrued and/or received due to intercompany arrangements					27		10
AEGON USA Realty Advisors, LLC
Related Party Transaction [Line Items]
Expense incurred as result of multiple service agreements				50	44	101	86
AEGON USA Investment Management LLC
Related Party Transaction [Line Items]
Expense incurred as result of multiple service agreements				439	511	930	1,003
Transamerica Capital, Inc.
Related Party Transaction [Line Items]
Expense incurred as result of multiple service agreements				6,129	5,984	11,687	12,136
Transamerica Asset Management, Inc.
Related Party Transaction [Line Items]
Expense incurred as result of multiple service agreements				0	5	79	82
Distribution and shareholder services agreement
Related Party Transaction [Line Items]
Revenue from participation agreement				$ 598	$ 509	$ 1,198	$ 1,000
0.13% Note Receivable
Related Party Transaction [Line Items]
Intercompany short-term note payable/receivable			$ 25,000
Interest on intercompany note payable/receivable			0.13%
Intercompany short-term note receivable, date			Jun. 19, 2015
0.36% Note Receivable
Related Party Transaction [Line Items]
Intercompany short-term note payable/receivable			$ 25,000
Interest on intercompany note payable/receivable			0.36%
Intercompany short-term note receivable, date			Feb. 25, 2016
0.83% Note Payable
Related Party Transaction [Line Items]
Intercompany short-term note payable/receivable		$ 35,000
Interest on intercompany note payable/receivable		0.83%
0.9% Note Payable
Related Party Transaction [Line Items]
Intercompany short-term note payable/receivable	$ 3,000
Interest on intercompany note payable/receivable	0.90%