Related Party Transactions - Additional Information (Detail) - USD ($) $ in Thousands							12 Months Ended
	Oct. 20, 2017	Aug. 09, 2017	Aug. 04, 2017	Jun. 20, 2017	May 22, 2017	Jun. 19, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Expense incurred as result of multiple service agreements							$ 11,554	$ 10,223	$ 10,818
Period of bear interest at commercial paper rate							30 days
Due to affiliates							$ 6,148	5,064
Interest income accrued and/or received due to intercompany arrangements							7	31	18
Interest expense accrued and/or paid due to intercompany arrangements							137	0	0
AEGON USA Realty Advisors, LLC
Related Party Transaction [Line Items]
Expense incurred as result of multiple service agreements							168	181	149
AEGON USA Investment Management LLC
Related Party Transaction [Line Items]
Expense incurred as result of multiple service agreements							2,716	1,927	1,709
Transamerica Capital, Inc.
Related Party Transaction [Line Items]
Expense incurred as result of multiple service agreements							23,901	24,501	30,356
Transamerica Asset Management, Inc.
Related Party Transaction [Line Items]
Expense incurred as result of multiple service agreements							79	320	361
Distribution and shareholder services agreement
Related Party Transaction [Line Items]
Revenue from participation agreement							2,752	$ 2,199	$ 2,381
Transamerica Life Insurance Company
Related Party Transaction [Line Items]
Expense incurred as result of multiple service agreements							$ 73
0.83% Note Payable
Related Party Transaction [Line Items]
Intercompany short-term note payable/receivable		$ 20,000	$ 15,000		$ 35,000
Interest on intercompany note payable/receivable					0.83%
Intercompany short-term note receivable, date					May 22, 2017
0.9% Note Payable
Related Party Transaction [Line Items]
Intercompany short-term note payable/receivable		$ 3,000		$ 3,000
Interest on intercompany note payable/receivable				0.90%
Intercompany short-term note receivable, date				Jun. 20, 2017
1.1% Note Payable
Related Party Transaction [Line Items]
Intercompany short-term note payable/receivable	$ 10,000
Interest on intercompany note payable/receivable	1.10%
Intercompany short-term note receivable, date	Oct. 20, 2017
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