Investments - Schedule of Unrealized Investment Losses by Class of Investment (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than Twelve Months	$ 209,731
Fair Value, Twelve Months or Longer	2,013,546
Fair Value, Total	2,223,277
Unrealized Loss Less Than Twelve Months	(1,062)
Unrealized Loss Twelve Months or Longer	(127,014)
Unrealized Loss Total	(128,076)
Fixed Maturities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than Twelve Months	209,731
Fair Value, Twelve Months or Longer	2,013,546
Fair Value, Total	2,223,277
Unrealized Loss Less Than Twelve Months	(1,062)
Unrealized Loss Twelve Months or Longer	(127,014)
Unrealized Loss Total	(128,076)
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than Twelve Months	0
Fair Value, Twelve Months or Longer	0
Fair Value, Total	0
Unrealized Loss Less Than Twelve Months	0
Unrealized Loss Twelve Months or Longer	0
Unrealized Loss Total	0
U.S. Government Direct, Guaranteed, and Government-Sponsored Enterprises [Member] | Fixed Maturities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than Twelve Months	2,504
Fair Value, Twelve Months or Longer	369,854
Fair Value, Total	372,358
Unrealized Loss Less Than Twelve Months	(1)
Unrealized Loss Twelve Months or Longer	(32,106)
Unrealized Loss Total	(32,107)
States, Municipalities, and Political Subdivisions [Member] | Fixed Maturities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than Twelve Months	5,096
Fair Value, Twelve Months or Longer	47,379
Fair Value, Total	52,475
Unrealized Loss Less Than Twelve Months	(73)
Unrealized Loss Twelve Months or Longer	(1,616)
Unrealized Loss Total	(1,689)
Foreign Governments [Member] | Fixed Maturities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than Twelve Months	901
Fair Value, Twelve Months or Longer	4,589
Fair Value, Total	5,490
Unrealized Loss Less Than Twelve Months	(2)
Unrealized Loss Twelve Months or Longer	(1)
Unrealized Loss Total	(3)
Corporates [Member] | Fixed Maturities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than Twelve Months	197,051
Fair Value, Twelve Months or Longer	1,507,916
Fair Value, Total	1,704,967
Unrealized Loss Less Than Twelve Months	(964)
Unrealized Loss Twelve Months or Longer	(79,680)
Unrealized Loss Total	(80,644)
Collateralized Debt Obligations [Member] | Fixed Maturities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than Twelve Months	0
Fair Value, Twelve Months or Longer	13,250
Fair Value, Total	13,250
Unrealized Loss Less Than Twelve Months	0
Unrealized Loss Twelve Months or Longer	(7,210)
Unrealized Loss Total	(7,210)
Other Asset-backed Securities [Member] | Fixed Maturities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than Twelve Months	0
Fair Value, Twelve Months or Longer	2,913
Fair Value, Total	2,913
Unrealized Loss Less Than Twelve Months	0
Unrealized Loss Twelve Months or Longer	(21)
Unrealized Loss Total	(21)
Redeemable Preferred Stocks [Member] | Fixed Maturities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than Twelve Months	4,179
Fair Value, Twelve Months or Longer	67,645
Fair Value, Total	71,824
Unrealized Loss Less Than Twelve Months	(22)
Unrealized Loss Twelve Months or Longer	(6,380)
Unrealized Loss Total	$ (6,402)