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CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Statement of Comprehensive Income [Abstract]        
Net unrealized gain (loss) on available-for-sale securities, tax benefit (provision) $ 0 $ 200,000 $ (100,000) $ 600,000