Condensed Consolidated Statements of Comprehensive Income (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Statement of Other Comprehensive Income [Abstract]
Net income	$ 23,477	$ 25,153	$ 73,091	$ 73,933
Available for sale securities:
Unrealized gains (losses) arising during the period	5,878	1,863	(35,342)	(2,167)
Reclassification adjustment for net gains realized in earnings (net of tax expense $1 and $8 for the three months ended September 30, 2013 and 2012, respectively, and net of tax expense of $7 and $480 for the nine months ended September 30, 2013 and 2012, respectively)	(2)	(13)	(11)	(719)
Income tax (expense) benefit related to unrealized losses	(2,351)	(745)	14,137	867
Net change in unrealized gains	3,525	1,105	(21,216)	(2,019)
Held to maturity securities:
Accretion of unrealized losses related to factors other than credit to investment securities held to maturity (net of tax benefit of $7 and $23 for the three months ended September 30, 2013 and 2012, respectively, and net of tax benefit of $29 and $76 for the nine months ended September 30, 2013 and 2012, respectively)	11	35	43	114
Net change in unrealized losses related to factors other than credit	11	35	43	114
Other comprehensive income (loss), net of tax	3,536	1,140	(21,173)	(1,905)
Comprehensive income	$ 27,013	$ 26,293	$ 51,918	$ 72,028