CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $)	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 11,225,000		$ 10,928,000
Investments available-for-sale:
Net change in unrealized gains (losses) on investments available-for-sale	4,634,000		7,132,000
Related income tax (expense) benefit	(1,841,000)		(2,823,000)
Net investment gains reclassified into earnings	0		0
Related income tax expense	0		0
Net effect on other comprehensive income (loss)	2,793,000		4,309,000
Defined benefit pension plan:
Recognition of unrealized gain (loss)	292,000	[1]	48,000	[1]
Related income tax (expense) benefit	(116,000)		(37,000)
Net effect on other comprehensive income (loss)	176,000		11,000
Total other comprehensive income (loss)	2,969,000		4,320,000
Comprehensive income	$ 14,194,000		$ 15,248,000

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