Basic and Diluted Net Income Per Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Basic and Diluted Net Income Per Common Share
Net income available to common shareholders									$ 45,713	$ 23,272	$ 39,224
Weighted Average Shares Outstanding
Basic (in shares)	54,265,000	53,900,000	53,799,000	53,620,000	55,390,000	56,682,000	56,639,000	56,512,000	53,897,834	56,304,636	56,243,015
Effect of Dilutive Securities (in shares)									773,195	530,924	750,933
Diluted (in shares)	55,160,000	54,764,000	54,547,000	54,200,000	55,837,000	57,197,000	57,190,000	57,124,000	54,671,029	56,835,560	56,993,948
Basic net income per common share (in dollars per share)	$ 0.20	$ 0.22	$ 0.24	$ 0.18	$ 0.16	$ (0.08)	$ 0.19	$ 0.14	$ 0.85	$ 0.41	$ 0.70
Diluted net income per common share (in dollars per share)	$ 0.20	$ 0.22	$ 0.24	$ 0.18	$ 0.16	$ (0.08)	$ 0.19	$ 0.14	$ 0.84	$ 0.41	$ 0.69
Antidilutive options excluded from calculation of net income per common share (in shares)									0	341,277	131,890