Supplementary Data on Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	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, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities
Net income	$ 21,040	$ 21,984	$ 16,183	$ 34,275	$ 30,068	$ 25,357	$ 20,452	$ 28,366	$ 34,287	$ 23,599	$ 25,995	$ 27,012	$ 93,482	$ 104,243	$ 110,893
Adjustments to reconcile net income to net cash provided by operating activities:
Realized investment gains													(12,713)	(10,917)	(22,245)
Increase in accrued investment income													(2,566)	(5,563)	(1,898)
(Decrease) increase in accrued expenses													(5,798)	1,513	1,157
Depreciation and amortization													7,734	7,958	7,680
Increase in insurance liabilities													145,313	153,423	143,542
Increase in premium receivables													(8,641)	(3,638)	(4,018)
Increase in deferred policy acquisition costs													(8,981)	(12,662)	(14,659)
(Increase) decrease in reinsurance recoverables													(748)	1,570	(1,289)
Increase in income tax liabilities													8,935	9,745	7,099
Debt retirement costs													2,338	0	0
Other													(11,312)	(23,739)	(20,326)
Total adjustments													113,561	117,690	95,043
Net cash provided by operating activities													$ 207,043	$ 221,933	$ 205,936