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
Mar. 31, 2017
Mar. 31, 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 1,060 5,679
Balance at end of period 539,542 510,860
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 (4,089) (2,331)
OCI, before Reclassifications, before Tax, Attributable to Parent 1,620 9,723
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent 269  
Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent 1,351  
AOCI before Tax, Attributable to Parent (2,738) 7,392
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
OCI, before Reclassifications, before Tax, Attributable to Parent 0 0
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent 0  
Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent 0  
AOCI before Tax, Attributable to Parent 0 9
AOCI Attributable to Parent [Member]    
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]    
AOCI Tax, Attributable to Parent 1,695 2,007
Balance at beginning of period (2,394) (315)
Other comprehensive (loss) income before reclassification, tax (560) (4,044)
Reclassification from accumulated other comprehensive income, tax 0  
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent 269  
Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent (560)  
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent 791  
AOCI Tax, Attributable to Parent 1,135 (2,037)
Balance at end of period $ (1,603) $ 5,364