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)
Balance at Dec. 31, 2012	$ 879,485	$ 1,755	$ 329,452	$ (155,801)	$ 628,871	$ 75,208
Balance (in shares) at Dec. 31, 2012		17,558,046		3,511,380
Net income	49,133				49,133
Changes in other comprehensive income:
Change in net unrealized gain (loss) on investments	(34,172)					(34,172)
Change in net non-credit other-than-temporary impairment losses	248					248
Change in foreign currency translation gain (loss)	209					209
Other comprehensive income (loss)	(33,715)					(33,715)
Shares issued under stock plan (in shares)		100,246
Shares issued under stock plan	1,488	10	1,478
Share-based compensation	3,491		3,491
Balance at Sep. 30, 2013	$ 899,882	$ 1,765	$ 334,421	$ (155,801)	$ 678,004	$ 41,493
Balance (in shares) at Sep. 30, 2013		17,658,292		3,511,380