Consolidated Statements of Stockholders' Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock	Additional Paid-in Capital	Treasury Stock	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning balance at Dec. 31, 2013	$ 902,212	$ 1,770	$ 335,546	$ (155,801)	$ 692,337	$ 28,360
Beginning balance (in shares) at Dec. 31, 2013		17,709,876		3,511,380
Net income	76,054				76,054
Changes in other comprehensive income:
Change in net unrealized gain (loss) on investments	15,312					15,312
Change in net non-credit other-than-temporary impairment losses	103					103
Change in foreign currency translation gain (loss)	(4,956)					(4,956)
Total other comprehensive income	10,459					10,459
Shares issued under stock plan (in shares)		68,255
Shares issued under stock plan	(582)	7	(589)
Share-based compensation	8,450		8,450
Ending balance at Sep. 30, 2014	$ 996,593	$ 1,777	$ 343,407	$ (155,801)	$ 768,391	$ 38,819
Ending balance (in shares) at Sep. 30, 2014		17,778,131		3,511,380