Stockholders' Equity (Schedule of Stock Options) (Details) - $ / shares		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Number of Option Shares
Exercised (in shares)		(505,312)	(476,047)	(681,426)
Balance at end of the period (in shares)	[1]	212,030
Exercisable at December 31, 2015 (in shares)	[1]	162,170
Equity Plan
Number of Option Shares
Balance at beginning of the period (in shares)		453,331	723,661	1,320,819
Exercised (in shares)		(214,601)	(258,530)	(574,288)
Forfeited (in shares)		(26,700)	(11,800)	(22,870)
Reduction for cash dividend (in shares)		0	0
Balance at end of the period (in shares)		212,030	453,331	723,661	1,320,819
Exercisable at December 31, 2015 (in shares)		162,170
Weighted Average Exercise Price
Balance at beginning of the period (in usd per share)		$ 16.89	$ 15.46	$ 19.92
Exercised (in usd per share)		14.48	12.89	23.04
Forfeited (in usd per share)		14.30	16.93	19.36
Reduction for cash dividend (in usd per share)		(2.00)	(2.00)
Balance at end of the period (in usd per share)		15.38	16.89	15.46	$ 19.92
Exercisable at December 31, 2015 (in usd per share)		14.83
Outstanding exercise price (minimum, in usd per share)		15.49	6.09	8.09	10.09
Outstanding exercise price (maximum, in usd per share)		19.17	19.17	29.11	$ 31.11
Exercised (minimum, in usd per share)		6.09	8.09	8.09
Exercised (maximum, in usd per share)		19.17	29.11	31.11
Forfeited (minimum, in usd per share)		6.09	8.09	10.09
Forfeited (maximum, in usd per share)		19.17	29.11	$ 31.11
Reduction for cash dividend (minimum, in usd per share)			6.09
Reduction for cash dividend (maximum, in usd per share)			$ 19.17
Exercisable (minimum, in usd per share)		15.49
Exercisable (maximum, in usd per share)		$ 19.17

[1] The aggregate intrinsic value for option shares outstanding and option shares exercisable is $9.6 million and $7.5 million, respectively. The weighted average remaining term for option shares outstanding and option shares exercisable is 1.4 years and 1.2 years, respectively.