CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income		$ 15,112	$ 10,813
Investments available-for-sale:
Net change in unrealized gains on investments available-for-sale		1,502	10,655
Related income tax (expense) benefit		(598)	(4,232)
Net investment gains reclassified into earnings		(2)	(1,769)
Related income tax expense (benefit)		0	705
Net effect on other comprehensive income (loss)		902	5,359
Defined benefit pension plan:
Recognition of unrealized loss (gain)	[1]	295	284
Related income tax expense (benefit)		(117)	(113)
Net effect on other comprehensive income for the period		178	171
Total other comprehensive income (loss)		1,080	5,530
Comprehensive income		$ 16,192	$ 16,343

[1] This amount is included in the computation of net periodic benefit cost, see Note 9.