CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement of Comprehensive Income [Abstract]
Net income/ (loss)	$ (14,338)	$ 28,276	$ (4,351)	$ 58,593
Investments available-for-sale:
Net change in unrealized gains on investments available-for-sale	11,366	7,167	25,629	15,981
Related income tax expense	(2,891)	(1,873)	(6,515)	(4,179)
Net investment gains reclassified into earnings	(212)	(5)	(381)	(5)
Related income tax expense	55	1	97	1
Net effect on other comprehensive income for the period	8,318	5,290	18,830	11,798
Defined benefit pension plan:
Recognition of unrealized loss	218	265	437	530
Related income tax benefit	(56)	(70)	(111)	(139)
Net effect on other comprehensive income for the period	162	195	326	391
Total other comprehensive income	8,480	5,485	19,156	12,189
Comprehensive income/ (loss)	$ (5,858)	$ 33,761	$ 14,805	$ 70,782