Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Intangibles, accumulated amortization	$ 4,640	$ 3,683
Deferred income taxes, valuation allowance	$ 0	$ 1,626
Preferred stock, par value (in USD per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, Class A, par value $0.01 per share; 150,000,000 shares authorized; 28,363,879 and 28,073,438 shares issued, 27,657,435 and 27,487,257 shares outstanding at December 31, 2015 and 2014, respectively
Common stock, par value (in USD per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	150,000,000	150,000,000
Common stock, shares issued (in shares)	28,363,879	28,073,438
Common stock, shares outstanding (in shares)	27,657,435	27,487,257
Common stock, Class B, par value $0.01 per share; 30,000,000 shares authorized; 3,813,884 shares issued and outstanding at December 31, 2015 and 2014, respectively
Common stock, par value (in USD per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	30,000,000	30,000,000
Common stock, shares issued (in shares)	3,813,884	3,813,884
Common stock, shares outstanding (in shares)	3,813,884	3,813,884
5 3/4% Senior Notes due 2019
Debt instrument interest rate	5.75%	5.75%
8 1/2% Senior Notes due 2020
Debt instrument interest rate	8.50%	8.50%
7% Senior Notes due 2022
Debt instrument interest rate	7.00%	7.00%