Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Statement of Income and Comprehensive Income [Abstract]
Net income	$ 10,613	$ 13,303	$ 39,620	$ 38,074
Other comprehensive gain, net of tax [Abstract]
Unrealized holding losses arising during period, net of relcassification adjustments for amounts included in net income	60	(31)	80	(9)
Comprehensive income	$ 10,673	$ 13,272	$ 39,700	$ 38,065