Condensed Consolidated Statements of Comprehensive Income (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Statement of Other Comprehensive Income [Abstract]
Net income	$ 26,253	$ 23,277	$ 49,614	$ 48,780
Available for sale securities:
Unrealized losses arising during the period	(36,793)	(6,050)	(41,220)	(4,029)
Reclassification adjustment for net gains realized in earnings (net of tax expense $3 and $412 for the three months ended June 30, 2013 and 2012, respectively, and net of tax expense of $6 and $471 for the six months ended June 30, 2013 and 2012, respectively)	(5)	(618)	(9)	(707)
Income tax benefit related to unrealized losses	14,717	2,420	16,488	1,612
Net change in unrealized gains	(22,081)	(4,248)	(24,741)	(3,124)
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 $10 and $25 for the three months ended June 30, 2013 and 2012, respectively, and net of tax benefit of $21 and $53 for the six months ended June 30, 2013 and 2012, respectively)	14	38	32	79
Net change in unrealized losses related to factors other than credit	14	38	32	79
Other comprehensive income, net of tax	(22,067)	(4,210)	(24,709)	(3,045)
Comprehensive income	$ 4,186	$ 19,067	$ 24,905	$ 45,735