Stock-Based Compensation - Summary of Activity of Non-Performance Based and Performance Based Options (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Non-Performance Based [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Under option, beginning of year, Shares	115,459	148,498	187,032
Granted, Shares	0	0	0
Exercised, Shares	(25,395)	(27,657)
Forfeited, Shares	(1,953)	(5,382)	(38,534)
Under option, end of year, Shares	88,111	115,459	148,498
Exercisable at end of year, Shares	88,111	115,459	148,498
Under option, beginning of year, Weighted-Average Exercise Price	$ 17.24	$ 16.37	$ 15.32
Granted, Weighted-Average Exercise Price	$ 0	$ 0	$ 0
Exercised, Weighted-Average Exercise Price	$ 14.81	$ 13.29
Forfeited, Weighted-Average Exercise Price	$ 14.88	$ 13.43	$ 11.28
Under option, end of year, Weighted-Average Exercise Price	$ 18.00	$ 17.24	$ 16.37
Exercisable at end of year, Weighted-Average Exercise Price	$ 18.00	$ 17.24	$ 16.37
Under option, end of year, Weighted Average Contractual Term	2 years 8 months 16 days	3 years 15 days	3 years 4 months 2 days
Exercised, Aggregate Intrinsic Value	$ 148	$ 107
Exercisable at end of year, Weighted Average Contractual Term	2 years 8 months 16 days	3 years 15 days	3 years 4 months 2 days
Under option, end of year, Aggregate Intrinsic Value	884	641	1
Exercisable at end of year, Aggregate Intrinsic Value	884	641	1
Performance Based [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Under option, beginning of year, Shares	371,000	391,321	393,891
Granted, Shares	0	0	0
Exercised, Shares	(6,477)	(4,524)
Forfeited, Shares	(5,192)	(15,797)	(2,570)
Under option, end of year, Shares	359,331	371,000	391,321
Exercisable at end of year, Shares	341,030	351,856	369,766
Under option, beginning of year, Weighted-Average Exercise Price	$ 16.76	$ 16.43	$ 16.45
Granted, Weighted-Average Exercise Price	$ 0	$ 0	$ 0
Exercised, Weighted-Average Exercise Price	$ 11.05	$ 7.47
Forfeited, Weighted-Average Exercise Price	$ 25.51	$ 13.22	$ 19.67
Under option, end of year, Weighted-Average Exercise Price	$ 16.74	$ 16.76	$ 16.43
Exercisable at end of year, Weighted-Average Exercise Price	$ 17.23	$ 17.27	$ 17.05
Under option, end of year, Weighted Average Contractual Term	2 years 1 month 10 days	3 years 1 month 13 days	4 years 1 month 28 days
Exercised, Aggregate Intrinsic Value	72	42
Exercisable at end of year, Weighted Average Contractual Term	2 years	3 years 4 days	4 years 18 days
Under option, end of year, Aggregate Intrinsic Value	2,955	1,401	774
Exercisable at end of year, Aggregate Intrinsic Value	$ 2,629	$ 1,145	$ 435