CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Net income	$ 16,154	$ 2,229	$ 1,014	$ 10,595	$ 15,835	$ 7,199	$ 6,212	$ 14,273	$ 29,992		$ 43,519		$ 37,966
OTHER COMPREHENSIVE INCOME (LOSS)
Change in unrealized holding gains (losses) on investment securities, net of deferred income tax expense (benefit) of $18,664, $(8,390) and $12,849									34,663		(15,582)		23,863
Reclassification adjustment for realized investment gains included in net income, net of income tax expense of $(2,518), $(3,149) and $(2,806)									(4,677)		(5,848)		(5,211)
Reclassification adjustment for amounts amortized into net periodic pension and postretirement benefit cost (income), net of deferred income tax (expense) benefit of $(955), $765 and $950:
Net actuarial loss									375		1,882		2,108
Prior service credit									(2,149)		(460)		(344)
Total reclassification adjustment associated with affiliate's pension and postretirement benefit plans									(1,774)		1,422		1,764
Change in funded status of affiliate's pension and postretirement benefit plans, net of deferred income tax expense (benefit) of $(2,994), $16,836 and $(2):
Net actuarial gain (loss)									(5,525)		13,718		(736)
Prior service (cost) credit									(35)		17,548		732
Total change in funded status of affiliate's pension and postretirement benefit plans									(5,560)		31,266		(4)
Other comprehensive income									22,652	[1]	11,258	[1]	20,412
Total comprehensive income									$ 52,644		$ 54,777		$ 58,378

[1] All amounts are net of tax. Amounts in parentheses indicate debits.