CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income		$ 10,813	$ 11,225
Investments available-for-sale:
Net change in unrealized gains on investments available-for-sale		10,655	4,634
Related income tax (expense) benefit		(4,232)	(1,841)
Net investment gains reclassified into earnings		(1,769)	0
Tax expense		705	0
Net effect on other comprehensive income (loss)		5,359	2,793
Defined benefit pension plan:
Recognition of unrealized gain (loss)	[1]	284	292
Related income tax (expense) benefit		(113)	(116)
Net effect on other comprehensive income for the period		171	176
Total other comprehensive income (loss)		5,530	2,969
Comprehensive income		$ 16,343	$ 14,194

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