Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Condensed Consolidated Balance Sheets
Due from charterers, reserve	$ 408	$ 488
Vessels, accumulated depreciation	663,055	597,214
Deferred drydock, accumulated amortization	10,403	8,086
Other assets, accumulated amortization	16,853	13,162
Fixed assets, accumulated depreciation and amortization	$ 3,765	$ 3,311
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	100,000,000	100,000,000
Common stock, shares issued (in shares)	44,461,157	44,270,273
Common stock, shares outstanding (in shares)	44,461,157	44,270,273