CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 50,657	$ 24,826	$ 117,581	$ 71,976
Other comprehensive (loss) income, net of tax
Unrealized gain (loss) on debt securities arising during the period	(10,185)	1,501	(28,993)	7,064
Change in retirement obligation	347	213	1,164	615
Unrealized gain (loss) on derivatives	99	129	414	385
Other comprehensive income (loss)	(9,739)	1,843	(27,415)	8,064
Comprehensive income	$ 40,918	$ 26,669	$ 90,166	$ 80,040

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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