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Nature of operations (Details) (USD $) In Thousands, except Share data, unless otherwise specified | 0 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Apr. 17, 2012 | Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011 | Aug. 02, 2010 private_equity_funds
Equity [Line Items] |  |  |  |  |
Number of private equity funds (in private equity funds) |  |  |  |  | 3
Common stock share price (in dollars per share) | $ 20.00 |  |  |  |
Proceeds from issuance of initial public offering | $ 256,400 | $ 0 | $ 256,381 | $ 0 |
Proceeds from concurrent private placement | 50,000 | 0 | 50,000 | 0 |
IPO [Member] |  |  |  |  |
Equity [Line Items] |  |  |  |  |
Stock issued during the period (in shares) | 13,889,470 |  |  |  |
Private Placement [Member] |  |  |  |  |
Equity [Line Items] |  |  |  |  |
Stock issued during the period (in shares) | 2,666,666 |  |  |  |
Stockholder [Member] |  |  |  |  |
Equity [Line Items] |  |  |  |  |
Proceeds from issuance of initial public offering | $ 147,200 |  |  |  |
Stockholder [Member] | IPO [Member] |  |  |  |  |
Equity [Line Items] |  |  |  |  |
Stock issued during the period (in shares) | 7,900,000 |  |  |  |
Underwriters With An Option To Purchase Shares [Member] | IPO [Member] |  |  |  |  |
Equity [Line Items] |  |  |  |  |
Stock issued during the period (in shares) | 2,842,104 |  |  |  |

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- Definition The cash inflow associated with the amount received from entity's first offering of stock to the public. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Financing Activities -URI http://asc.fasb.org/extlink&oid=6513228 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 14 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3255-108585 + Details
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- Definition The cash inflow associated with the amount received from entity's raising of capital via private rather than public placement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Financing Activities -URI http://asc.fasb.org/extlink&oid=6513228 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 14 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3255-108585 + Details
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