Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Investments, Owned, Federal Income Tax Note [Line Items]
Federal statutory rate			35.00%	35.00%
Income tax expense (benefit)	$ 0	$ 0	$ 575,000	$ 0
Valuation allowance for deferred tax assets	132,382,000		132,382,000		$ 154,440,000
Unrecognized income tax benefit, net	4,391,000		4,391,000		4,391,000	$ 3,404,000
Unrecognized income tax benefit, gross	12,547,000		12,547,000		12,547,000
Operating loss carry forward	583,938,000		$ 583,938,000		627,860,000
Operating loss carry forward, expiration period			15 years
Alternative minimum tax credit carry forward	4,216,000		$ 4,216,000		4,216,000
Penalties expense related to federal income tax	0	0
Interest expense (income) related to federal income tax	21,000	$ 18,000	58,000	$ 63,000
Interest payable arising from income tax examinations	219,000		219,000		161,000
Return of capital to Transamerica Corporation			(44,800,000)		(13,381,000)
Foreign
Investments, Owned, Federal Income Tax Note [Line Items]
Tax credit carry forward	9,946,000		$ 9,946,000		$ 9,776,000
Foreign tax credit carry forward, expiration date in year			10 years		10 years
Capital Loss Carry forward
Investments, Owned, Federal Income Tax Note [Line Items]
Tax credit carry forward	$ 84,000		$ 84,000		$ 84,000
Capital loss tax credit carry forward, expiration date in year			5 years		5 years
Capital loss tax credit carry forward, expiration year			2018
Earliest Tax Year
Investments, Owned, Federal Income Tax Note [Line Items]
Operating loss carry forward, expiration year			2023
Latest Tax Year
Investments, Owned, Federal Income Tax Note [Line Items]
Operating loss carry forward, expiration year			2031
Latest Tax Year | Foreign
Investments, Owned, Federal Income Tax Note [Line Items]
Foreign tax credit carry forward, expiration year			2027