CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 116,433	$ 100,864	$ 53,209
Investments available-for-sale:
Net change in unrealized gains/(losses) on investments available-for-sale	14,429	(9,925)	(294)
Related income tax expense/ (benefit)	(3,742)	2,600	108
Net investment gains reclassified into earnings	(77)	(190)	(1,273)
Related income tax expense	20	50	504
Net effect on other comprehensive income/(loss)	10,630	(7,465)	(955)
Defined benefit pension plan:
Recognition of unrealized (loss)	1,175	135	1,202
Related income tax (expense)	(383)	(90)	(490)
Net effect on other comprehensive income	792	45	712
Total other comprehensive income/(loss)	11,422	(7,420)	(243)
Comprehensive income	$ 127,855	$ 93,444	$ 52,966