Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Other comprehensive income (loss):
Other comprehensive income (loss), before tax	$ (2,905)	$ 6,273	$ 31,919	$ 501
Other comprehensive income (loss):
Other comprehensive income (loss), tax (expense) benefit	897	(2,013)	(9,866)	(121)
Net of Tax
Stockholders equity, beginning of period			1,119,241	955,738
Other comprehensive income (loss):
Other comprehensive income (loss), net of tax	(2,008)	4,260	22,053	380
Stockholders equity, end of period	1,310,215		1,310,215
Accumulated Other Comprehensive Income (Loss)
Before Tax
AOCI before tax, beginning of period	35,485	940	661	6,712
Other comprehensive income (loss):
AOCI before tax, end of period	32,580	7,213	32,580	7,213
Tax Effect
AOCI tax effect, beginning of period	(11,523)	(153)	(760)	(2,045)
Other comprehensive income (loss):
AOCI tax effect, end of period	(10,626)	(2,166)	(10,626)	(2,166)
Net of Tax
Stockholders equity, beginning of period	23,962	787	(99)	4,667
Other comprehensive income (loss):
Stockholders equity, end of period	21,954	5,047	21,954	5,047
Accumulated Net Investment Gains (Losses) On Investments
Other comprehensive income (loss):
Unrealized holding gains (losses) arising during the period, before tax	(2,470)	6,821	33,415	2,266
Less: Reclassification adjustment for gains included in net income, before tax	(435)	(548)	(1,496)	(1,765)
Other comprehensive income (loss), before tax	(2,905)	6,273	31,919	501
Other comprehensive income (loss):
Unrealized holding gains (losses) arising during the period, tax (expense) benefit	752	(2,144)	(10,278)	(593)
Less: Reclassification adjustment for gains included in net income, tax (expense) benefit	145	131	412	472
Other comprehensive income (loss), tax (expense) benefit	897	(2,013)	(9,866)	(121)
Other comprehensive income (loss):
Unrealized holding gains (losses) arising during the period, net of tax	(1,718)	4,677	23,137	1,673
Less: Reclassification adjustment for gains included in net income, net of tax	(290)	(417)	(1,084)	(1,293)
Other comprehensive income (loss), net of tax	$ (2,008)	$ 4,260	$ 22,053	$ 380