Annual report pursuant to Section 13 and 15(d)

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Accumulated Other Comprehensive Income (Details)

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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Accumulated Other Comprehensive Income (Details) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Accumulated other comprehensive income $ 171,051 $ 218,067 $ 210,122 $ 258,328
Net unrealized gain on securities        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Accumulated other comprehensive income 1,370 1,168    
Accumulated Other Comp. Income (Loss)        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Accumulated other comprehensive income $ 1,370 $ 1,168 $ 33,297 $ 65,865