Accumulated Other Comprehensive Income by Component (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	$ 1,106,392
Total other comprehensive income (loss), net of taxes	5,988	$ 39,744
Balance at end of period	1,123,756		$ 1,106,392
Unrealized Holding Gains (Losses) on AFS Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	104,538	95,533	95,533
OCI before reclassifications	5,919	44,320
Amounts reclassified from AOCI	532	1,869
Net current period OCI	6,451	46,189
Tax expense (benefit)	0	0
Total other comprehensive income (loss), net of taxes	6,451	46,189
Balance at end of period	110,989	141,722	104,538
Unrealized Holding Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(1,225)	4,202	4,202
OCI before reclassifications	161	(1,150)
Amounts reclassified from AOCI	247	(197)
Net current period OCI	408	(1,347)
Tax expense (benefit)	0	0
Total other comprehensive income (loss), net of taxes	408	(1,347)
Balance at end of period	(817)	2,855	(1,225)
OCI Adjustments for Policy holder liabilities, VOBA, and Deferred Tax
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(47,963)	(43,144)	(43,144)
OCI before reclassifications	(871)	(5,098)
Net current period OCI	(871)	(5,098)
Tax expense (benefit)	0	0
Total other comprehensive income (loss), net of taxes	(871)	(5,098)
Balance at end of period	(48,834)	(48,242)	(47,963)
Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	55,350	56,591	56,591
OCI before reclassifications	5,209	38,072
Amounts reclassified from AOCI	779	1,672
Net current period OCI	5,988	39,744
Tax expense (benefit)	0	0
Total other comprehensive income (loss), net of taxes	5,988	39,744	(1,241)
Balance at end of period	$ 61,338	$ 96,335	$ 55,350