Earnings per Common Share (Details) (USD $) Share data in Thousands, except Per 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
Earnings per Common Share [Abstract]
Conversion value of notes to invoke inclusion in dilutive securities incremental shares issuable									$ 1,000
Net income	$ 16,678,000	$ 12,205,000	$ 12,637,000	$ 10,842,000	$ 8,811,000	$ 13,753,000	$ 9,706,000	$ 3,108,000	$ 52,362,000	$ 35,378,000	$ 43,013,000
Net income per share [Abstract]
Basic (in dollars per share)	$ 0.17	$ 0.13	$ 0.13	$ 0.11	$ 0.09	$ 0.14	$ 0.10	$ 0.03	$ 0.54	$ 0.37	$ 0.45
Diluted (in dollars per share)	$ 0.14	$ 0.11	$ 0.11	$ 0.10	$ 0.08	$ 0.12	$ 0.09	$ 0.03	$ 0.46	$ 0.32	$ 0.41
Shares used in computing net income per share [Abstract]
Weighted average basic shares outstanding (in shares)									96,181	95,189	94,549
Dilutive securities [Abstract]
Stock options and unvested RSAs (in shares)									4,516	4,289	3,281
Stock warrants (in shares)									6,702	6,564	6,082
Shares issuable on conversion of the Notes (in shares)									6,499	4,468	0
Total dilutive securities (in shares)									17,717	15,321	9,363
Weighted average diluted shares outstanding (in shares)									113,898	110,510	103,912