Loss Reserves - Reconciliation of Beginning and Ending Balances (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 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	80,416	92,479
Prior years	(52,797)	(7,467)
Total losses incurred	27,619	85,012
Losses and LAE paid in respect of default notices received in:
Current year	331	204
Prior years	127,224	221,457
Reinsurance terminations	0	(4)
Total losses paid	127,555	221,657
Net reserve at end of period	1,288,384	1,712,270
Plus reinsurance recoverables	46,658	41,119
Reserve at end of period	$ 1,335,042	$ 1,753,389