Consolidated Statement 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, 2014	$ 1,027,224	$ 1,778	$ 347,022	$ (155,801)	$ 787,666	$ 46,559
Beginning balance (in shares) at Dec. 31, 2014		17,792,846		3,511,380
Net income	25,929				25,929
Changes in other comprehensive income:
Change in net unrealized gain (loss) on investments	1,904					1,904
Change in net non-credit other- than-temporary impairment losses	15					15
Change in foreign currency translation gain (loss)	(796)					(796)
Total other comprehensive income	1,123					1,123
Shares issued under stock plan (in shares)		110,352
Shares issued under stock plan	(4,147)	11	(4,158)
Share-based compensation	3,474		3,474
Ending balance at Mar. 31, 2015	$ 1,053,603	$ 1,789	$ 346,338	$ (155,801)	$ 813,595	$ 47,682
Ending balance (in shares) at Mar. 31, 2015		17,903,198		3,511,380