Quarterly report pursuant to Section 13 or 15(d)

Accumulated Other Comprehensive Income - Activity in Accumulated Other Comprehensive Income (Detail)

v3.7.0.1
Accumulated Other Comprehensive Income - Activity in Accumulated Other Comprehensive Income (Detail) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]        
Balance at beginning of period     $ 531,025 $ 493,918
OCI, before Reclassifications, Net of Tax, Attributable to Parent $ 2,678 $ 3,757 3,737 9,436
Balance at end of period 550,140 525,185 550,140 525,185
Accumulated Net Unrealized Investment Gain (Loss) [Member]        
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]        
AOCI before Tax, Attributable to Parent (2,737) 7,392 (4,089) (2,331)
OCI, before Reclassifications, before Tax, Attributable to Parent 3,910 6,424 5,530 16,147
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent (938)   (1,206)  
Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent 2,972   4,324  
AOCI before Tax, Attributable to Parent 235 13,816 235 13,816
Accumulated Net Unrealized Investment Gain (Loss) [Member] | Interest-Only Strip [Member]        
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]        
AOCI before Tax, Attributable to Parent 0 9 0 9
OCI, before Reclassifications, before Tax, Attributable to Parent 0 (9) 0 (9)
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent 0   0  
Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent 0   0  
AOCI before Tax, Attributable to Parent 0 0 0 0
AOCI Attributable to Parent [Member]        
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]        
AOCI Tax, Attributable to Parent 1,134 (2,037) 1,695 2,007
Balance at beginning of period (1,603) 5,364 (2,394) (315)
Other comprehensive (loss) income before reclassification, tax (1,232) (2,658) (1,793) (6,702)
Reclassification from accumulated other comprehensive income, tax 0   0  
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent (938)   (1,206)  
Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent (1,232)   (1,793)  
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent 1,740   2,531  
AOCI Tax, Attributable to Parent (98) (4,695) (98) (4,695)
Balance at end of period $ 137 $ 9,121 $ 137 $ 9,121