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	27,847				27,847
Changes in other comprehensive income:
Change in net unrealized gain (loss) on investments	(39,773)					(39,773)
Change in net non-credit other-than-temporary impairment losses	303					303
Change in foreign currency translation gain (loss)	1,579					1,579
Other comprehensive income (loss)	(37,891)					(37,891)
Shares issued under stock plan (in shares)		86,997
Shares issued under stock plan	1,037	9	1,028
Share-based compensation	3,474		3,474
Balance at Jun. 30, 2013	$ 873,952	$ 1,764	$ 333,954	$ (155,801)	$ 656,718	$ 37,317
Balance (in shares) at Jun. 30, 2013		17,645,043		3,511,380