Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Comprehensive Income [Abstract]
Net income	$ 147,520	$ 98,361	$ 101,891
Available for sale securities:
Unrealized gains (losses) arising during the period	31,215	(48,755)	(12,004)
Reclassification adjustment for net gains realized in earnings (net of tax expense $1,162, $84, and $1,609 in 2014, 2013, and 2012, respectively)	(1,742)	(125)	(2,414)
Income tax (expense) benefit related to unrealized gains (losses)	(12,486)	19,502	4,802
Net change in unrealized gains (losses)	16,987	(29,378)	(9,616)
Held to maturity securities:
Reclassification adjustment for impairments realized in net income (net of tax benefit of $42 in 2012)	0	0	62
Accretion of unrealized losses related to factors other than credit to investment securities held to maturity (net of tax benefit of $37, $37, and $84 in 2014, 2013, and 2012, respectively)	57	56	126
Net change in unrealized losses related to factors other than credit	57	56	188
Other comprehensive income (loss), net of tax	17,044	(29,322)	(9,428)
Comprehensive income	$ 164,564	$ 69,039	$ 92,463