Loss Reserves - Reconciliation of Beginning and Ending Balances (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 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	158,906	196,543
Prior years	(103,948)	(64,941)
Total losses incurred	54,958	131,602
Losses and LAE paid in respect of default notices received in:
Current year	2,125	1,396
Prior years	298,847	392,007
Reinsurance terminations	0	(4)
Total losses paid	300,972	393,399
Net reserve at end of period	1,142,306	1,587,118
Plus reinsurance recoverables	44,783	45,215
Reserve at end of period	$ 1,187,089	$ 1,632,333