Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Other comprehensive income (loss):
Other comprehensive income (loss), before tax		$ 15,751	$ (12,771)	$ 34,824	$ (5,772)
Other comprehensive income (loss):
Other comprehensive income (loss), tax (expense) benefit		(5,049)	4,002	(10,763)	1,892
Net of Tax
Stockholders equity, beginning of period				1,119,241	955,738
Other comprehensive income (loss):
Other comprehensive income (loss), net of tax		10,702	(8,769)	24,061	(3,880)
Stockholders equity, end of period		1,248,607		1,248,607
Accumulated Net Investment Gains (Losses) On Investments
Other comprehensive income (loss):
Unrealized holding gains (losses) arising during the period, before tax		16,334	(12,203)	35,885	(4,555)
Less: Reclassification adjustment for gains included in net income, before tax	[1]	(583)	(568)	(1,061)	(1,217)
Other comprehensive income (loss), before tax		15,751	(12,771)	34,824	(5,772)
Other comprehensive income (loss):
Unrealized holding gains (losses) arising during the period, tax (expense) benefit		(5,185)	3,888	(11,030)	1,551
Less: Reclassification adjustment for gains included in net income, tax (expense) benefit	[1]	136	114	267	341
Other comprehensive income (loss), tax (expense) benefit		(5,049)	4,002	(10,763)	1,892
Other comprehensive income (loss):
Unrealized holding gains (losses) arising during the period, net of tax		11,149	(8,315)	24,855	(3,004)
Less: Reclassification adjustment for gains included in net income, net of tax	[1]	(447)	(454)	(794)	(876)
Other comprehensive income (loss), net of tax		10,702	(8,769)	24,061	(3,880)
Accumulated Other Comprehensive Income (Loss)
Before Tax
AOCI before tax, beginning of period		19,734	13,711	661	6,712
Other comprehensive income (loss):
AOCI before tax, end of period		35,485	940	35,485	940
Tax Effect
AOCI tax effect, beginning of period		(6,474)	(4,155)	(760)	(2,045)
Other comprehensive income (loss):
AOCI tax effect, end of period		(11,523)	(153)	(11,523)	(153)
Net of Tax
Stockholders equity, beginning of period		13,260	9,556	(99)	4,667
Other comprehensive income (loss):
Stockholders equity, end of period		$ 23,962	$ 787	$ 23,962	$ 787

[1] Included in net realized investment gains on our condensed consolidated statements of comprehensive income.