Accumulated Other Comprehensive Income by Component (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 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	$ 18,401	$ 35,339	24,389	$ 75,083
Balance at end of period	1,134,892		1,134,892		$ 1,106,392
Unrealized Holding Gains (Losses) on AFS Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	110,989	141,722	104,538	95,533	95,533
OCI before reclassifications	19,197	40,786	25,116	88,654
Amounts reclassified from AOCI	(611)	68	(79)	(1,611)
Net current period OCI	18,586	40,854	25,037	87,043
Tax expense (benefit)	0	0	0	0
Total other comprehensive income (loss), net of taxes	18,586	40,854	25,037	87,043
Balance at end of period	129,575	182,576	129,575	182,576	104,538
Unrealized Holding Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(817)	2,855	(1,225)	4,202	4,202
OCI before reclassifications	2,530	1,290	2,691	140
Amounts reclassified from AOCI	373	513	620	316
Net current period OCI	2,903	1,803	3,311	456
Tax expense (benefit)	0	0	0	0
Total other comprehensive income (loss), net of taxes	2,903	1,803	3,311	456
Balance at end of period	2,086	4,658	2,086	4,658	(1,225)
OCI Adjustments for Policy holder liabilities, VOBA, and Deferred Tax
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(48,834)	(48,242)	(47,963)	(43,144)	(43,144)
OCI before reclassifications	(3,088)	(7,318)	(3,959)	(12,416)
Net current period OCI	(3,088)	(7,318)	(3,959)	(12,416)
Tax expense (benefit)	0	0	0	0
Total other comprehensive income (loss), net of taxes	(3,088)	(7,318)	(3,959)	(12,416)
Balance at end of period	(51,922)	(55,560)	(51,922)	(55,560)	(47,963)
Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	61,338	96,335	55,350	56,591	56,591
OCI before reclassifications	18,639	34,758	23,848	76,378
Amounts reclassified from AOCI	(238)	581	541	(1,295)
Net current period OCI	18,401	35,339	24,389	75,083
Tax expense (benefit)	0	0	0	0
Total other comprehensive income (loss), net of taxes	18,401	35,339	24,389	75,083	(1,241)
Balance at end of period	$ 79,739	$ 131,674	$ 79,739	$ 131,674	$ 55,350