Consolidated Statement of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands		Total	Common Stock	Additional Paid-in Capital	Treasury Stock	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning Balance at Dec. 31, 2014		$ 1,027,224	$ 3,556	$ 345,244	$ (155,801)	$ 787,666	$ 46,559
Beginning Balance (in shares) at Dec. 31, 2014			35,586		7,023
Net Income		81,057				81,057
Changes in Comprehensive Income (Loss):
Change in Net Unrealized Gain (Loss) on Investments		(22,389)					(22,389)
Change in Net Non-Credit Other-Than- Temporary Impairment Losses		56					56
Change in Foreign Currency Translation Gain (Loss)		(622)					(622)
Total Comprehensive Income (Loss)		(22,955)					(22,955)
Shares Issued	[1]	(4,175)	$ 30	(4,205)
Shares Issued (in shares)	[1]		299
Share-Based Compensation		14,997		14,997
Ending Balance at Dec. 31, 2015		1,096,148	$ 3,586	356,036	$ (155,801)	868,723	23,604
Ending Balance (in shares) at Dec. 31, 2015			35,885		7,023
Net Income		82,726				82,726
Dividends Declared	[2]	(3,930)				(3,930)
Changes in Comprehensive Income (Loss):
Change in Net Unrealized Gain (Loss) on Investments		(5,355)					(5,355)
Change in Net Non-Credit Other-Than- Temporary Impairment Losses		(50)					(50)
Change in Foreign Currency Translation Gain (Loss)		(9,324)					(9,324)
Total Comprehensive Income (Loss)		(14,729)					(14,729)
Shares Issued	[1]	349	$ 26	323
Shares Issued (in shares)	[1]		262
Share-Based Compensation		17,624		17,624
Ending Balance at Dec. 31, 2016		$ 1,178,188	$ 3,612	373,983	$ (155,801)	947,519	8,875
Ending Balance (in shares) at Dec. 31, 2016		36,147	36,147		7,023
Net Income		$ 40,494				40,494
Dividends Declared	[2]	(6,633)				(6,633)
Changes in Comprehensive Income (Loss):
Change in Net Unrealized Gain (Loss) on Investments		9,023					9,023
Change in Net Non-Credit Other-Than- Temporary Impairment Losses		40					40
Change in Foreign Currency Translation Gain (Loss)		1,930					1,930
Total Comprehensive Income (Loss)		10,993					10,993
Shares Issued	[1]	(10,906)	$ 38	(10,944)
Shares Issued (in shares)	[1]		383
Share-Based Compensation		13,829		13,829
Ending Balance at Dec. 31, 2017		$ 1,225,965	$ 3,650	$ 376,868	$ (155,801)	$ 981,380	$ 19,868
Ending Balance (in shares) at Dec. 31, 2017		36,530	36,530		7,023

[1] Includes shares issued under the Second Amended and Restated 2005 Stock Incentive Plan, to directors and the Employees Stock Purchase Plan.

[2] Dividends Declared were $0.225 per share and $0.135 per share for the years ended December 31, 2017 and 2016, respectively. There were no dividends declared in 2015.