Related Party Transactions - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Related Party Transaction [Line Items]
Expense incurred as result of multiple service agreements	$ 2,738	$ 2,800	$ 5,501	$ 5,507
Period of bear interest at commercial paper rate			30 days
Due to affiliates	19,316		$ 19,316		$ 6,148
Interest expense accrued and/or paid due to intercompany arrangements	37	44	91	51
Interest income accrued and/or received due to intercompany arrangements	1	6	2	6
AEGON USA Realty Advisors, LLC
Related Party Transaction [Line Items]
Expense incurred as result of multiple service agreements	10	50	21	101
AEGON USA Investment Management LLC
Related Party Transaction [Line Items]
Expense incurred as result of multiple service agreements	541	439	1,158	930
Transamerica Capital, Inc.
Related Party Transaction [Line Items]
Expense incurred as result of multiple service agreements	5,814	6,129	11,924	11,687
Transamerica Asset Management, Inc.
Related Party Transaction [Line Items]
Expense incurred as result of multiple service agreements		0	0	79
Distribution and shareholder services agreement
Related Party Transaction [Line Items]
Revenue from participation agreement	786	$ 598	1,597	$ 1,198
Transamerica Life Insurance Company
Related Party Transaction [Line Items]
Expense incurred as result of multiple service agreements	$ 195		313
1.10 % Note Payable
Related Party Transaction [Line Items]
Intercompany short-term note payable or receivable			$ 10,000
Interest on intercompany note payable/receivable			1.10%
Intercompany short-term note receivable, date			Oct. 20, 2017