Reclassifications Out of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other net realized investment (gains) losses									$ (16,451)	$ 4,182	$ 28,454
Income (loss) before income taxes	$ (86,602)	$ 436	$ 5,793	$ 4,448	$ (10,304)	$ (16,779)	$ 7,753	$ 9,280	(75,925)	(10,050)	47,618
Income tax expense (benefit)									19,229	499	2,250
Net income (loss)	$ (73,317)	$ 3,728	$ 7,192	$ 5,701	$ (22,998)	$ (8,924)	$ 10,089	$ 12,282	(56,696)	(9,551)	$ 49,868
Total reclassifications, net of tax									2,450	(848)
Reclassification out of Accumulated Other Comprehensive Income | Unrealized Gains and Losses on Available for Sale Securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other net realized investment (gains) losses									2,467	(3,921)
Other than temporary impairment losses on investments									456	2,606
Income (loss) before income taxes									2,923	(1,315)
Income tax expense (benefit)									(473)	686
Net income (loss)									2,450	(629)
Reclassification out of Accumulated Other Comprehensive Income | Foreign Currency Items
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other net realized investment (gains) losses									0	(336)
Income tax expense (benefit)									0	117
Net income (loss)									$ 0	$ (219)