Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance, beginning of period at Dec. 31, 2014		$ 522	$ 353,337	$ 795,740	$ 95,527
Repurchases of common stock		(45)	(207,714)
Share-based compensation			33,544
Net issuance of common stock		6	(6)
Adjustments to paid-in capital, other			1,089
Net income	$ 189,871			189,871
Dividends				(32,807)
Change in foreign currency translation adjustment, net of income tax expense (benefit)					(41,482)
Change in net unrealized investment gains (losses) not-other-than temporarily impaired					(42,201)
Change in net unrealized investment gains (losses) other-than-temporarily impaired					391
Balance, end of period at Dec. 31, 2015	1,145,772	483	180,250	952,804	12,235
Repurchases of common stock		(33)	(153,994)
Share-based compensation			26,219
Net issuance of common stock		7	(7)
Net income	219,414			219,414
Dividends				(33,367)
Change in foreign currency translation adjustment, net of income tax expense (benefit)					6,608
Change in net unrealized investment gains (losses) not-other-than temporarily impaired					10,745
Change in net unrealized investment gains (losses) other-than-temporarily impaired					10
Balance, end of period at Dec. 31, 2016	1,221,374	457	52,468	1,138,851	29,598
Repurchases of common stock		(19)	(78,558)	(78,195)
Share-based compensation			26,095
Net issuance of common stock		5	$ (5)
Net income	350,255			350,255
Dividends				(35,821)
Change in foreign currency translation adjustment, net of income tax expense (benefit)					17,188
Change in net unrealized investment gains (losses) not-other-than temporarily impaired					(3,166)
Change in net unrealized investment gains (losses) other-than-temporarily impaired					(52)
Balance, end of period at Dec. 31, 2017	$ 1,419,101	$ 443		$ 1,375,090	$ 43,568