Quarterly report pursuant to Section 13 or 15(d)

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

v3.10.0.1
Accumulated Other Comprehensive Income - Activity in Accumulated Other Comprehensive Income (Detail) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jan. 01, 2018
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]          
Balance at end of period   $ (13,092) $ 235 $ (13,092) $ 235
Balance at beginning of period $ 562,477     562,477 531,025
Other comprehensive (loss) income, net of tax   (1,117) 1,740 (7,438) 2,531
Balance at end of period   571,707 550,140 571,707 550,140
Accumulated Net Unrealized Investment Gain (Loss) [Member]          
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]          
Balance at beginning of period (3,188) (11,523) (2,737) (3,188) (4,089)
Other comprehensive income before reclassification, before tax   (1,502) 3,910 (10,366) 5,530
Reclassification from accumulated other comprehensive income, before tax   67 938 67 1,206
Adjustment to accumulated other comprehensive income related to adoption of ASU 2016-01 and 2018-02, before tax 529     529  
Period change, before tax   (1,569) 2,972 (9,904) 4,324
Balance at end of period   (13,092) 235 (13,092) 235
Tax Expense Benefit [Member]          
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]          
Balance at beginning of period, tax 1,319 3,316 1,134 1,319 1,695
Other comprehensive (loss) income before reclassification, tax   452 (1,232) 2,995 (1,793)
Reclassification from accumulated other comprehensive income, tax   0 0 0 0
Adjustment to accumulated other comprehensive income related to adoption of ASU 2016-01 and 2018-02, tax (546)     (546)  
Period change, tax   452 (1,232) 2,449 (1,793)
Balance at end of period, tax   3,768 (98) 3,768 (98)
AOCI Attributable to Parent [Member]          
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]          
Balance at beginning of period (1,869) (8,207) (1,603) (1,869) (2,394)
Other comprehensive income before reclassification, net of tax   (1,050) 2,678 (7,371) 3,737
Reclassification from accumulated other comprehensive income   (67) (938) (67) (1,206)
Adjustment to accumulated other comprehensive income related to adoption of ASU 2016-01 and 2018-02, net of tax $ (17)     (17)  
Other comprehensive (loss) income, net of tax   (1,117) 1,740 (7,455) 2,531
Balance at end of period   $ (9,324) $ 137 $ (9,324) $ 137