Earnings per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Numerator [Abstract]
Net income attributable to CAI common stockholders used in the calculation of basic and diluted earnings per share	$ 17,411	$ 16,528	$ 15,135	$ 14,391	$ 12,891	$ 13,622	$ 10,880	$ 12,796	$ 63,465	$ 50,189	$ 28,383
Denominator [Abstract]
Weighted average shares used in the calculation of basic earnings per share (in shares)									19,495,000	19,295,000	17,974,000
Dilutive Securities Included In Computation Of Earnings Per Share [Line Items]
Weighted average shares used in the calculation of diluted earnings per share (in shares)									19,945,000	19,693,000	18,203,000
Net income per share attributable to CAI common stockholders [Abstract]
Basic (in dollars per share)	$ 0.87	$ 0.86	$ 0.78	$ 0.75	$ 0.67	$ 0.71	$ 0.56	$ 0.66	$ 3.26	$ 2.60	$ 1.58
Diluted (in dollars per share)	$ 0.85	$ 0.84	$ 0.77	$ 0.73	$ 0.66	$ 0.70	$ 0.55	$ 0.65	$ 3.18	$ 2.55	$ 1.56
Stock options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities having antidilutive effect (in shares)									363,000	232,500	493,000
Restricted common stock [Member]
Dilutive Securities Included In Computation Of Earnings Per Share [Line Items]
Effect of dilutive securities (in shares)									0	0	3,000
Stock options [Member]
Dilutive Securities Included In Computation Of Earnings Per Share [Line Items]
Effect of dilutive securities (in shares)									450,000	398,000	226,000