CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 11,142	$ 12,089	$ 29,052	$ 34,809
Investments available-for-sale:
Net change in unrealized gains (losses) on investments available-for-sale	(2,714)	(1,032)	10,779	(24,925)
Related income tax (expense) benefit	1,061	407	(4,284)	9,935
Net investment gains reclassified into earnings	8		8	118
Related income tax expense	(3)		(3)	(47)
Net effect on other comprehensive income (loss) for the period	(1,648)	(625)	6,500	(14,919)
Defined benefit pension plan:
Recognition of unrealized gain	67	249	183	1,176
Related income tax benefit	(20)	(91)	(81)	(461)
Net effect on other comprehensive income (loss) for the period	48	158	102	715
Total other comprehensive income (loss)	(1,600)	(467)	6,602	(14,204)
Comprehensive income	$ 9,541	$ 11,622	$ 35,654	$ 20,605