Supplementary Data on Cash Flows (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended												12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Cash flows from operating activities
Net income	$ 34,287	$ 23,599	$ 25,995	$ 27,012	$ 31,826	$ 32,266	$ 13,103	$ 26,671	$ 32,913	$ 23,637	$ (11,851)	$ 25,807	$ 110,893	$ 103,866	$ 70,506
Adjustments to reconcile net income to net cash provided by operating activities:
Realized investment gains													(22,245)	(27,298)	(37,663)
Increase in accrued investment income													(1,898)	(2,618)	(7,348)
Increase (decrease) in accrued expenses													1,157	13,589	(9,203)
Depreciation and amortization													7,680	7,892	8,577
Increase in insurance liabilities													143,542	127,992	105,576
Increase in premium receivables													(4,018)	(5,638)	(1,263)
Increase in deferred policy acquisition costs													(14,659)	(13,989)	(6,258)
(Increase) decrease in reinsurance recoverable													(1,289)	872	(2,877)
Increase in income tax liabilities													7,099	29,752	17,953
Other													(20,326)	(31,572)	(22,121)
Total adjustments													95,043	98,982	45,373
Net cash provided by operating activities													$ 205,936	$ 202,848	$ 115,879