Consolidated Statements of Comprehensive Income (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Consolidated Statements of Comprehensive Income [Abstract]
Net income	$ 20,387	$ 6,968
Change in unrealized gain on investments:
Unrealized gain arising during the period	275	1,274
Call and repayment losses charged to investment income	15
Reclassification adjustment for realized gains	(20)	(21)
Net change in unrealized gain	270	1,253
Deferred income taxes on above change	(105)	(483)
Total other comprehensive income	165	770
Comprehensive income	$ 20,552	$ 7,738