Schedule II Financial Information of Registrant Parent Company Balance Sheet (Details) - USD ($) $ / shares in Units, $ in Thousands		Dec. 31, 2016	Dec. 31, 2015
Assets
Fixed-maturities available for sale—at fair value (amortized cost $2,856,468 and $1,893,356)		$ 2,838,512	$ 1,865,461
Equity securities available for sale—at fair value (cost $1,330 and $75,538)		1,330	75,430
Trading securities—at fair value		879,862	1,279,137
Other short-term investments		741,531	1,076,944
Cash		52,149	46,898
Restricted cash		9,665	13,000
Investment in subsidiaries, at equity in net assets (Note C)		3,000,000
Property and equipment, at cost (less accumulated depreciation of $51,567 and $50,648)	[1],[2]	70,665	46,802
Other assets (Note E)		343,835	313,929
Total assets		5,863,174	5,642,100
Liabilities and Stockholders’ Equity
Long-term debt (Note 12)		1,069,537	1,219,454
Other liabilities		321,859	269,016
Total liabilities		2,990,888	3,145,169
Common stock: par value $.001 per share; 485,000,000 shares authorized at December 31, 2016 and 2015; 232,091,921 and 224,432,465 shares issued at December 31, 2016 and 2015, respectively; 214,521,079 and 206,871,768 shares outstanding at December 31, 2016 and 2015, respectively		232	224
Treasury stock, at cost: 17,570,842 and 17,560,697 shares at December 31, 2016 and 2015, respectively		(893,332)	(893,176)
Additional paid-in capital		2,779,891	2,716,618
Retained earnings		997,890	691,742
Accumulated other comprehensive income (loss) (“AOCI”) (Note 17)		(12,395)	(18,477)
Total common stockholders’ equity		2,872,286	2,496,931
Liabilities and Equity		5,863,174	5,642,100
Balance Sheet Parentheticals [Abstract]
Property and Equipment, Owned, Accumulated Depreciation		$ 118,500	$ 106,900
Common Stock, Par or Stated Value Per Share		$ 0.001	$ 0.001
Common Stock, Shares Authorized		485,000,000	485,000,000
Common Stock, Shares, Issued		232,091,921	224,432,465
Common Stock, Shares, Outstanding		214,521,079	206,871,768
Treasury Stock, Shares		17,570,842	17,560,697
Investments		$ 4,462,430	$ 4,298,686
Parent Company
Condensed Financial Statements, Captions [Line Items]
Notes Receivable, Related Parties			300,000
Assets
Fixed-maturities available for sale—at fair value (amortized cost $2,856,468 and $1,893,356)		79,336	41,176
Equity securities available for sale—at fair value (cost $1,330 and $75,538)		0	25,510
Trading securities—at fair value		0	5,482
Other short-term investments		311,418	158,658
Cash		8,256	3,301
Restricted cash		124	124
Investment in subsidiaries, at equity in net assets (Note C)		3,383,089	3,001,846
Accounts and Notes Receivable, Net		305,316	631,636
Other assets (Note E)		166,098	124,983
Total assets		4,253,637	3,992,716
Liabilities and Stockholders’ Equity
Long-term debt (Note 12)		1,069,537	1,219,454
Federal income taxes—current and deferred		266,289	229,939
Other liabilities		45,525	46,392
Total liabilities		1,381,351	1,495,785
Common stock: par value $.001 per share; 485,000,000 shares authorized at December 31, 2016 and 2015; 232,091,921 and 224,432,465 shares issued at December 31, 2016 and 2015, respectively; 214,521,079 and 206,871,768 shares outstanding at December 31, 2016 and 2015, respectively		232	224
Treasury stock, at cost: 17,570,842 and 17,560,697 shares at December 31, 2016 and 2015, respectively		(893,332)	(893,176)
Additional paid-in capital		2,779,891	2,716,618
Retained earnings		997,890	691,742
Accumulated other comprehensive income (loss) (“AOCI”) (Note 17)		(12,395)	(18,477)
Total common stockholders’ equity		2,872,286	2,496,931
Liabilities and Equity		$ 4,253,637	$ 3,992,716
Balance Sheet Parentheticals [Abstract]
Common Stock, Par or Stated Value Per Share		$ 0.001	$ 0.001
Common Stock, Shares Authorized		485,000,000	485,000,000
Common Stock, Shares, Issued		232,091,921	208,601,020
Common Stock, Shares, Outstanding		214,521,079	191,053,530
Treasury Stock, Shares		17,570,842	17,547,490
Investments		$ 390,754	$ 230,826

[1] Includes $49.7 million and $35.9 million in 2016 and 2015, respectively, related to our technology upgrade project.

[2] Property and equipment at cost, less accumulated depreciation of $118.5 million and $106.9 million at December 31, 2016 and 2015, respectively. Depreciation expense was $11.7 million, $6.7 million and $4.2 million for the years ended December 31, 2016, 2015 and 2014 respectively.