Accumulated Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Reclassifications out of accumulated other comprehensive income
Gains on investment securities available-for-sale	$ 963	$ 0
Income before income taxes	21,239	19,395
Income tax expense	(7,607)	(6,991)
Net income	13,632	12,404
Unrealized gains and losses on available-for-sale securities | Amount Reclassified from Accumulated Other Comprehensive Income
Reclassifications out of accumulated other comprehensive income
Gains on investment securities available-for-sale	963	0
Income before income taxes	963	0
Income tax expense	(361)	0
Net income	$ 602	$ 0