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 9 Months Ended
Jan. 01, 2018
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]          
Balance at end of period   $ (15,861) $ 497 $ (15,861) $ 497
Balance at beginning of period $ 562,477     562,477 531,025
Other comprehensive (loss) income, net of tax   (1,971) 153 (9,409) 2,684
Balance at end of period   567,748 559,247 567,748 559,247
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) (13,092) 235 (3,188) (4,089)
Other comprehensive income before reclassification, before tax   (2,750) 529 (13,115) 6,059
Reclassification from accumulated other comprehensive income, before tax   (19) (267) (87) (1,473)
Adjustment to accumulated other comprehensive income related to adoption of ASU 2016-01 and 2018-02, before tax 529     529  
Period change, before tax   (2,769) 262 (12,673) 4,586
Balance at end of period   (15,861) 497 (15,861) 497
Tax Expense Benefit [Member]          
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]          
Balance at beginning of period, tax 1,319 3,768 (98) 1,319 1,695
Other comprehensive (loss) income before reclassification, tax   798 (109) 3,793 (1,902)
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   798 (109) 3,247 (1,902)
Balance at end of period, tax   4,566 (207) 4,566 (207)
Accumulated Other Comprehensive Income (Loss) [Member]          
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]          
Balance at beginning of period (1,869) (9,324) 137 (1,869) (2,394)
Other comprehensive income before reclassification, net of tax   (1,952) 420 (9,322) 4,157
Reclassification from accumulated other comprehensive income   (19) (267) (87) (1,473)
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   (1,971) 153 (9,426) 2,684
Balance at end of period   $ (11,295) $ 290 $ (11,295) $ 290