Stock-Based Compensation - Summary of Stock Options Outstanding and Exercisable by Stock Option Plan (Details) - $ / shares	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2013
Outstanding Stock Options, Number of Options Outstanding	158,248	160,748	164,229	309,479
Outstanding Stock Options, Weighted Average Exercise Price	$ 25.06	$ 25.28	$ 25.28	$ 19.75
Exercisable Stock Options Exercisable, Number of Options Exercisable	133,665		113,072
Exercisable Stock Options Exercisable, Weighted Average Exercise Price	$ 29.13		$ 35.20
1995 Stock Option Plan [Member]
Outstanding Stock Options, Number of Options Outstanding	8,750
Outstanding Stock Options, Weighted Average Exercise Price	$ 31.20
Exercisable Stock Options Exercisable, Number of Options Exercisable	8,750
Exercisable Stock Options Exercisable, Weighted Average Exercise Price	$ 31.20
2004 Stock Option Plan [Member]
Outstanding Stock Options, Number of Options Outstanding	69,500
Outstanding Stock Options, Weighted Average Exercise Price	$ 10.10
Exercisable Stock Options Exercisable, Number of Options Exercisable	51,167
Exercisable Stock Options Exercisable, Weighted Average Exercise Price	$ 12.74
2004 Director's Plan [Member]
Outstanding Stock Options, Number of Options Outstanding	74,998
Outstanding Stock Options, Weighted Average Exercise Price	$ 39.68
Exercisable Stock Options Exercisable, Number of Options Exercisable	72,498
Exercisable Stock Options Exercisable, Weighted Average Exercise Price	$ 40.90
2013 Plan [Member]
Outstanding Stock Options, Number of Options Outstanding	5,000
Outstanding Stock Options, Weighted Average Exercise Price	$ 2.99
Exercisable Stock Options Exercisable, Number of Options Exercisable	1,250
Exercisable Stock Options Exercisable, Weighted Average Exercise Price	$ 2.99