Loss Reserves - Reconciliation of Beginning and Ending Balances (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Loss Reserve [Roll Forward]
Reserve at beginning of period	$ 1,438,813	$ 1,893,402
Less reinsurance recoverable	50,493	44,487
Net reserve at beginning of period	1,388,320	1,848,915
Losses and LAE incurred in respect of default notices received in:
Current year	219,485	292,090
Prior years	(134,780)	(99,591)
Total losses incurred	84,705	192,499
Losses and LAE paid in respect of default notices received in:
Current year	5,474	5,942
Prior years	407,977	549,706
Reinsurance terminations (2)	301	(2,854)
Total losses paid	413,752	552,794
Net reserve at end of period	1,059,273	1,488,620
Plus reinsurance recoverables	45,878	46,863
Reserve at end of period	$ 1,105,151	$ 1,535,483