CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 21,665	$ 15,112
Investments available-for-sale:
Net change in unrealized gains on investments available-for-sale	(12,689)	1,502
Related income tax expense	3,321	(598)
Net investment gains reclassified into earnings	(63)	(2)
Related income tax expense	16	0
Net effect on other comprehensive income (loss)	(9,415)	902
Defined benefit pension plan:
Recognition of unrealized gain (loss)	250	295
Related income tax (expense) benefit	(119)	(117)
Net effect on other comprehensive income for the period	131	178
Total other comprehensive income	(9,284)	1,080
Comprehensive income	$ 12,381	$ 16,192

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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Amount, after tax, of gain (loss) for (increase) decrease in value of benefit obligation for change in actuarial assumptions and increase (decrease) in value of plan assets from experience different from that assumed of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

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Amount after tax and reclassification adjustments, of appreciation (loss) in value of unsold available-for-sale securities. Excludes amounts related to other than temporary impairment (OTTI) loss.

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