Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Net income	$ 17,992us-gaap_NetIncomeLoss	$ 13,803us-gaap_NetIncomeLoss
Unrealized gains (losses) on available-for-sale securities arising during the period	1,450	1,313
Reclassification adjustment for gains	(14)	(83)
Other comprehensive income (loss) before income taxes	1,436	1,230
Tax effect	(530)	(454)
Other comprehensive income (loss), net of tax	906	776
Comprehensive income, net of tax	$ 18,898us-gaap_ComprehensiveIncomeNetOfTax	$ 14,579us-gaap_ComprehensiveIncomeNetOfTax

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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Amount before tax, after reclassification adjustments, of appreciation (loss) in value of unsold available-for-sale securities. Excludes amounts related to other than temporary impairment (OTTI) loss.

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Amount before tax of reclassification adjustment from accumulated other comprehensive income for unrealized gain (loss) realized upon the sale of available-for-sale securities.

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